MRI-guided catheters

ABSTRACT

An MRI-compatible catheter that reduces localized heating due to MR scanner-induced currents includes an elongated flexible shaft having a distal end portion and an opposite proximal end portion. A handle is attached to the proximal end portion and includes an electrical connector interface configured to be in electrical communication with an MRI scanner. One or more RF tracking coils are positioned adjacent the distal end portion of the shaft. Each RF tracking coil includes a conductive lead, such as a coaxial cable, that extends between the RF tracking coil and the electrical connector interface and electrically connects the RF tracking coil to an MRI scanner. In some embodiments of the present invention, the conductive lead has a length sufficient to define an odd harmonic/multiple of a quarter wavelength of the operational frequency of the MRI Scanner, and/or includes a series of pre-formed back and forth segments along its length.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/816,803, filed Jun. 16, 2010, which claims the benefit ofand priority to U.S. Provisional Patent Application No. 61/187,323 filedJun. 16, 2009, to U.S. Provisional Patent Application No. 61/219,638filed Jun. 23, 2009, and to U.S. Provisional Patent Application No.61/261,103 filed Nov. 13, 2009, the disclosures of which areincorporated herein by reference as if set forth in their entireties.This application also is a continuation-in-part of International PatentApplication No. PCT/US2012/026468, filed Feb. 24, 2012, which claims thebenefit of and priority to U.S. Provisional Patent Application No.61/446,329 filed Feb. 24, 2011.

FIELD OF THE INVENTION

The present invention relates to MRI-guided systems and may beparticularly suitable for MRI-guided cardiac systems such as EP systemsfor treating Atrial Fibrillation (AFIB).

BACKGROUND

Heart rhythm disorders (arrhythmias) occur when there is a malfunctionin the electrical impulses to the heart that coordinate how the heartbeats. During arrhythmia, a heart may beat too fast, too slowly orirregularly. Catheter ablation is a widely used therapy for treatingarrhythmias and involves threading a catheter through blood vessels of apatient and into the heart. In some embodiments, radio frequency (RF)energy may be applied through the catheter tip to destroy abnormal hearttissue causing the arrhythmia. In other embodiments a catheter tip maybe configured to cryogenically ablate heart tissue.

Guiding the placement of a catheter during ablation therapy within theheart is important. Conventional catheter ablation procedures areconducted using X-ray and/or ultrasound imaging technology to facilitatecatheter guidance and ablation of heart tissue. Conventional Cardiac EP(ElectroPhysiology) Systems are X-ray based systems which useelectroanatomical maps. Electroanatomical maps are virtualrepresentations of the heart showing sensed electrical activity.Examples of such systems include the Carto® electroanatomic mappingsystem from Biosense Webster, Inc., Diamond Bar, Calif., and the EnSiteNavX® system from Endocardial Solutions Inc., St. Paul, Minn.

Magnetic resonance imaging (MRI) has several distinct advantages overX-ray imaging technology, such as excellent soft-tissue contrast, theability to define any tomographic plane, and the absence of ionizingradiation exposure. In addition, MRI offers several specific advantagesthat make it especially well suited for guiding various devices used indiagnostic and therapeutic procedures including: 1) real-timeinteractive imaging, 2) direct visualization of critical anatomiclandmarks, 3) direct high resolution imaging, 4) visualization of adevice-tissue interface, 5) the ability to actively track deviceposition in three-dimensional space, and 6) elimination of radiationexposure.

Induced RF currents (referred to as RF coupling) on coaxial cables,electrical leads, guide wires, and other elongated devices utilized inMRI environments can be problematic. Such RF coupling may causesignificant image artifacts, and may induce undesired heating and causelocal tissue damage. To reduce the risk of tissue damage, it isdesirable to reduce or prevent patient contact with cables and otherconductive devices in an MRI environment. Such contact, however, may beunavoidable in some cases. For devices that are inserted inside thebody, such as endorectal, esophageal, and intravascular devices, therisk of tissue damage may increase.

SUMMARY

It should be appreciated that this Summary is provided to introduce aselection of concepts in a simplified form, the concepts being furtherdescribed below in the Detailed Description. This Summary is notintended to identify key features or essential features of thisdisclosure, nor is it intended to limit the scope of the invention.

In some embodiments of the present invention, an MRI-compatible ablationcatheter includes an elongated flexible shaft having a distal endportion, an opposite proximal end portion, and at least one lumenextending between the proximal and distal end portions. A handle isattached to the proximal end portion, and includes a main body portionand an actuator (e.g., a lever, piston, thumb slider, knob, etc.) incommunication with the shaft distal end portion and configured toarticulate the shaft distal end portion. In some embodiments, theactuator is a piston that is movable between extended and retractedpositions relative the handle main body portion. The handle includes anelectrical connector interface configured to be in electricalcommunication with an MRI scanner.

The distal end portion of the shaft includes an ablation tip and atleast one RF tracking coil positioned adjacent the ablation tip, andthat includes a conductive lead, such as a coaxial cable, extendingbetween the at least one RF tracking coil and the electrical connectorinterface and configured to electrically connect the at least onetracking coil to an MRI scanner. The conductive lead has a lengthsufficient to define an odd harmonic/multiple of a quarter wavelength ofthe operational frequency of the MRI Scanner. The at least one RFtracking coil also is electrically connected to a circuit that reducescoupling when the at least one RF tracking coil is exposed to an MRIenvironment. The shaft distal end portion also may include at least onesensing electrode configured to detect local electrical signals orproperties, and a thermocouple for measuring temperature. In someembodiments, the at least one RF tracking coil at the distal endupstream of an ablation electrode on the tip of the catheter comprises apair of RF tracking coils in adjacent spaced-apart relationship.

Each RF tracking coil can be about a 1-10 turn solenoid coil, and has alength in the longitudinal direction of the catheter of between about0.25 mm and about 4 mm. In some embodiments, each RF tracking coil isrecessed within the catheter shaft and a layer of MRI-compatiblematerial overlies the RF tracking coil and is substantially flush withan outer surface of the catheter shaft. This MRI-compatible material canserve the function of a heat sink for reducing heating.

A pull wire can extend through a shaft lumen and has a distal end and anopposite proximal end. An exemplary pull wire is a Kevlar string/cable.The pull wire distal end is attached to the shaft distal end portion andthe pull wire proximal end is attached to the piston. Movement of thepiston causes articulation of the shaft distal end portion to facilitatepositioning of the ablation tip during an ablation procedure. In someembodiments, the shaft distal end portion includes a biasing member thatis configured to urge the shaft distal end portion to a non-articulatedposition.

In some embodiments, the shaft distal end portion includes at least onefluid exit port in fluid communication with an irrigation lumen thatextends longitudinally through the catheter shaft lumen from the atleast one exit port to the proximal end portion of the catheter shaft.The irrigation lumen is in fluid communication with a fluid/solutionsource at the proximal end portion of the catheter shaft.

In some embodiments of the present invention, an MRI-compatible mappingcatheter includes an elongated flexible shaft having a distal endportion, an opposite proximal end portion, and at least one lumenextending between the proximal and distal end portions. A plurality ofsensing electrodes are arranged in spaced-apart relationship at theshaft distal end portion, and at least one RF tracking coil ispositioned at the shaft distal end portion and that includes aconductive lead configured to electrically connect the at least onetracking coil to an MRI scanner, wherein the conductive lead has alength sufficient to define an odd harmonic/multiple of a quarterwavelength of the operational frequency of the MRI Scanner. A handleattached to the proximal end portion and an actuator attached to thehandle is in communication with the shaft distal end portion. Activationof the actuator causes articulation of the shaft distal end portion.

Each RF tracking coil can be about a 1-10 turn solenoid coil, and has alongitudinal length of between about 0.25 mm and about 4 mm. In someembodiments, each RF tracking coil is recessed within the catheter shaftand a layer of MRI-compatible material overlies the RF tracking coil andis substantially flush with an outer surface of the catheter shaft.

A pull wire can extend through a shaft lumen and has a distal end and anopposite proximal end. The pull wire distal end is attached to the shaftdistal end portion and the pull wire proximal end is attached to thepiston. Movement of the piston causes articulation of the shaft distalend portion to facilitate positioning of the ablation tip during anablation procedure. In some embodiments, the shaft distal end portionincludes a biasing member that is configured to urge the shaft distalend portion to a non-articulated position.

According to some embodiments of the present invention, an MRI guidedinterventional system includes at least one catheter configured to beintroduced into a patient via a tortuous and/or natural lumen path, suchas the ablation catheter and mapping catheter described above. The atleast one catheter has an elongated flexible shaft with a distal endportion, an opposite proximal end portion, and at least one RF trackingcoil connected to a channel of an MRI scanner. A circuit is adapted tocommunicate with and/or reside in the MRI Scanner, and is configured to:(a) obtain MR image data and generate a series of near real time (RT)MRI images of target anatomy of a patient during a surgical procedureusing relevant anatomical scan planes associated with a 3-D MRI imagespace having a coordinate system; (b) identify coordinates associatedwith a location of at least a distal end portion of the at least onecatheter using the coordinate system of the 3-D MRI image space; and (c)render near RT interactive visualizations of the at least one catheterin the 3-D image space with RT image data of target patient anatomicalstructure and a registered pre-acquired first volumetric model of thetarget anatomical structure of the patient, wherein the circuitillustrates the at least one catheter with a physical representation inthe visualizations.

A display with a user interface in communication with the circuit isconfigured to display the visualizations during an MRI guidedinterventional procedure. The user interface is configured to allow auser to (a) rotate the visualizations and (b) alter a displayedvisualization to include only a near RT image of the target anatomy, toinclude the near RT image of the anatomy and the registered model of theanatomical structure, or to include only the registered model of theanatomical structure. The MRI Scanner is configured to interleave signalacquisition of tracking signals from the at least one tracking coil withimage data for the near RT MRI images, and the circuit is configured toelectronically track the at least one catheter in the 3-D image spaceindependent of scan planes used to obtain the MR image data so that theat least one catheter is not required to be in any of the relevantanatomical scan planes used to obtain MR image data for the at least onenear RT MRI image, and wherein the distal end portion of the at leastone catheter can take on a curvilinear shape. Also, the circuit isconfigured to calculate a device-tissue interface location proximate atip location of the at least one catheter in the three dimensional imagespace, and is configured to project axially forward a defined distancebeyond the tip to define the device-tissue interface. The calculatedtissue interface location is used to automatically define at least onescan plane used to obtain the MR image data during and/or proximate intime to a procedure using the at least one catheter.

According to some embodiments of the present invention, anMRI-compatible catheter that reduces localized heating due to MRscanner-induced currents includes an elongated flexible shaft having adistal end portion and an opposite proximal end portion. A handle isattached to the proximal end portion and includes an electricalconnector interface configured to be in electrical communication with anMRI scanner. One or more RF tracking coils are positioned adjacent thedistal end portion of the shaft. Each RF tracking coil includes aconductive lead, such as a coaxial cable, that extends between the RFtracking coil and the electrical connector interface and electricallyconnects the RF tracking coil to an MRI scanner. In some embodiments ofthe present invention, the conductive lead has a length sufficient todefine an odd harmonic/multiple of a quarter wavelength of theoperational frequency of the MRI Scanner, and/or includes a series ofpre-formed back and forth segments along its length. In some embodimentsof the present invention, the conductive lead is a coaxial cable thatincludes a self-resonant cable trap, such as, for example, a 60-turninductor.

In some embodiments of the present invention, the catheter includes oneor more sensing electrodes at the shaft distal end portion. One or moreof the sensing electrodes is electrically connected to a high impedanceresistor, for example, a resistor having an impedance of, for example,at least about 5,000 ohms.

In some embodiments of the present invention, the catheter includes atuning circuit that is configured to stabilize tracking signalsgenerated by one or more RF tracking coils. The tuning circuit may belocated within the handle of the catheter.

In some embodiments of the present invention, a sheath surrounds atleast a portion of the elongated shaft and includes at least one RFshield coaxially disposed therewithin. Each RF shield includes elongatedinner and outer tubular conductors. The inner and outer conductors eachhave respective opposite first and second end portions. An elongatedtubular dielectric layer of MRI compatible material is sandwichedbetween the inner and outer conductors and surrounds the innerconductor. Only the respective first end portions of the inner and outerconductors are electrically connected. The second end portions areelectrically isolated from each other. In some embodiments, the innerand outer conductors comprise conductive foil, conductive braid, or afilm with a conductive surface. A plurality of RF shields may bedisposed within the sheath in end-to-end spaced-apart relationship.

In some embodiments of the present invention, at least one RF shieldcoaxially disposed within the flexible shaft of the catheter. Each RFshield includes elongated inner and outer tubular conductors. The innerand outer conductors each have respective opposite first and second endportions. An elongated tubular dielectric layer of MRI compatiblematerial is sandwiched between the inner and outer conductors andsurrounds the inner conductor. Only the respective first end portions ofthe inner and outer conductors are electrically connected. The secondend portions are electrically isolated from each other. In someembodiments, the inner and outer conductors comprise conductive foil,conductive braid, or a film with a conductive surface. A plurality of RFshields may be disposed within the flexible shaft of the catheter inend-to-end spaced-apart relationship.

According to some embodiments of the present invention, the catheter isan ablation catheter with an ablation tip at the shaft distal endportion. An RF conductor extends longitudinally within the shaft fromthe ablation tip to the electrical connector interface at the handle andconnects the ablation tip to an RF generator. The RF conductor includesa series of pre-formed back and forth segments along its length.

According to some embodiments of the present invention, anMRI-compatible catheter that reduces localized heating due to MRscanner-induced currents includes an elongated flexible shaft having adistal end portion and an opposite proximal end portion. The catheterincludes an electrical connector interface that is configured to be inelectrical communication with an MRI scanner. The catheter also includesan ablation tip at the flexible shaft distal end portion, at least oneRF tracking coil positioned adjacent the flexible shaft distal endportion, and at least one sensing electrode at the shaft distal endportion. An RF conductor extends longitudinally within the flexibleshaft to the electrical connector interface and connects the ablationtip to an RF generator. In some embodiments, the RF conductor includes aseries of back and forth segments along its length.

A conductive lead extends between the at least one RF tracking coil andthe electrical connector interface and is configured to electricallyconnect the at least one tracking coil to the MRI scanner. In someembodiments, at least one self-resonant cable trap is in communicationwith the at least one RF tracking coil. An exemplary self-resonant cabletrap includes an inductor having between about twenty (20) turns andabout one-hundred (100) turns. In some embodiments, a self-resonantcable trap may include an inductor having about sixty (60) turns. Insome embodiments, the conductive lead includes a series of pre-formedback and forth segments along its length. In some embodiments, theconductive lead is a coaxial cable. In some embodiments, the conductivelead has a length sufficient to define an odd harmonic/multiple of aquarter wavelength of an operational frequency of the MRI Scanner.

According to some embodiments of the present invention, the at least oneRF tracking coil comprises a plurality of tracking coils, each attachedto a separate conductive lead, and wherein each conductive lead includesa series of back and forth segments along its length. In someembodiments, each conductive lead may have a length sufficient to definean odd harmonic/multiple of a quarter wavelength of an operationalfrequency of the MRI Scanner.

In some embodiments of the present invention, the at least one RFtracking coil comprises between 1-10 coil turns and/or has a lengthalong a longitudinal direction of the catheter of between about 0.25 mmand about 4 mm.

In some embodiments, at least one high impedance resistor is incommunication with the at least one sensing electrode.

In some embodiments, the ablation tip comprises platinum.

In some embodiments, the catheter includes at least one fluid exit portat the flexible shaft distal end portion. The at least one fluid exitport is in fluid communication with an irrigation lumen that extendslongitudinally through the flexible shaft from the at least one fluidexit port.

It is noted that aspects of the invention described with respect to oneembodiment may be incorporated in a different embodiment although notspecifically described relative thereto. That is, all embodiments and/orfeatures of any embodiment can be combined in any way and/orcombination. Applicant reserves the right to change any originally filedclaim or file any new claim accordingly, including the right to be ableto amend any originally filed claim to depend from and/or incorporateany feature of any other claim although not originally claimed in thatmanner. These and other objects and/or aspects of the present inventionare explained in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which form a part of the specification,illustrate some exemplary embodiments. The drawings and descriptiontogether serve to fully explain the exemplary embodiments.

FIG. 1 is a schematic illustration of an MRI-guided system configured toshow a device tissue interface using near RT MRI data according toembodiments of the present invention.

FIG. 2 is a schematic illustration of an intrabody device with atracking coil electrically connected to a Scanner channel according toembodiments of the present invention.

FIG. 3 is a schematic illustration of an MRI system with a workstationand display according to embodiments of the invention.

FIG. 4 is a circuit diagram of an exemplary tracking coil tuning circuitaccording to embodiments of the present invention.

FIGS. 5A-5D are contemplated screen shots of exemplary interactivevisualizations with a physical representation of an intrabody flexiblemedical device according to embodiments of the present invention.

FIG. 6 is a schematic illustration of a display with two viewingwindows, one showing an interactive visualization and the other showingat least one relevant near RT MRI image according to embodiments of thepresent invention.

FIGS. 7-21 are contemplated screen shots of exemplary visualizations andimages on a display and UI controls that can be generated to facilitatean MRI guided procedure according to embodiments of the presentinvention.

FIGS. 22A and 22B are exemplary (contemplated) screen shots of anintrabody device (e.g., ablation catheter) with the device rendered as aphysical representation and the MRI image being in close-up according toembodiments of the present invention.

FIGS. 23 and 24A-D are exemplary (contemplated) screen shotsillustrating navigational indicia that can be used to help guide and/orposition an intrabody device according to embodiments of the presentinvention.

FIGS. 25-28 are yet additional exemplary (contemplated) screen shotsillustrating patient data and target (clinician identified) treatmentzones that can provide information that can help drive clinicaldecisions according to embodiments of the present invention.

FIG. 29 is a schematic illustration of an MRI-interventional suiteaccording to embodiments of the present invention.

FIG. 30 is a schematic illustration of a data processing circuit orsystem according to embodiments of the present invention.

FIG. 31 is a perspective view of an exemplary ablation catheter,according to some embodiments of the present invention.

FIG. 32A is a partial perspective view of the distal end portion of theablation catheter of FIG. 31.

FIG. 32B illustrates the distal end portion of the ablation catheter ofFIG. 31 in an articulated configuration, according to some embodimentsof the present invention.

FIG. 33 is an enlarged partial perspective view of the tip portion ofthe ablation catheter of FIG. 31, according to some embodiments of thepresent invention.

FIG. 34 is a cross-sectional view of the tip portion of the ablationcatheter of FIG. 31 taken along lines 34-34.

FIG. 35 is a side view of the distal end portion of the ablationcatheter of FIG. 31, according to some embodiments of the presentinvention.

FIG. 36 is an enlarged partial view of the tip portion of the ablationcatheter of FIG. 35.

FIG. 37 is a cross-sectional view of the ablation catheter of FIG. 35taken along lines 37-37.

FIG. 38 is a cross-sectional view of the ablation catheter of FIG. 35taken along lines 38-38.

FIG. 39 is a cross-sectional view of the ablation catheter of FIG. 38taken along lines 39-39.

FIG. 40 is a cross-sectional view of the ablation catheter of FIG. 38 atthe same location as the cross-sectional view of FIG. 39 and thatillustrates an exemplary internal diameter of free space availableinside the tip assembly, according to some embodiments of the presentinvention.

FIG. 41 is a cross-sectional view of the ablation catheter of FIG. 35 atthe same location as the cross-sectional view of FIG. 37 and thatillustrates an exemplary internal diameter and wires/components insidethe catheter shaft lumen, according to some embodiments of the presentinvention.

FIG. 42 is a cross-sectional view of the ablation catheter of FIG. 35that illustrates an exemplary number of wires that can be placed insidethe catheter shaft lumen, according to some embodiments of the presentinvention.

FIG. 43 is a perspective view of the handle at the proximal end of theablation catheter of FIG. 31, according to some embodiments of thepresent invention, and with a cover removed.

FIG. 44 is an exploded perspective view of the handle of FIG. 43.

FIG. 45 illustrates the handle of FIG. 44 in an assembled configuration.

FIG. 46 is a schematic illustration of an exemplary tracking coilcircuit utilized in the ablation catheter of FIG. 31, according to someembodiments of the present invention.

FIG. 47A is an MRI image of the ablation catheter of FIG. 31 in a 3.0 TMRI environment with the RF tracking coil circuit of FIG. 46 not beingutilized with respective multiple RF tracking coils.

FIG. 47B illustrates MRI signal strength of the MRI image of FIG. 47A inthe Z direction.

FIG. 47C illustrates MRI signal strength of the MRI image of FIG. 47A inthe X direction.

FIG. 48A is an MRI image of the ablation catheter of FIG. 31 in a 3.0 TMRI environment with the RF tracking coil circuit of FIG. 46 beingutilized with respective multiple RF tracking coils, according to someembodiments of the present invention.

FIG. 48B illustrates MRI signal strength of the MRI image of FIG. 48A inthe Z direction.

FIG. 48C illustrates MRI signal strength of the MRI image of FIG. 48A inthe X direction.

FIG. 49 is a Smith chart illustrating input impedance of a ¾λ coaxialcable shorted at one end by a PIN diode, according to some embodimentsof the present invention.

FIG. 50 is a partial perspective view of the distal end of a mappingcatheter, according to some embodiments of the present invention.

FIG. 51A is a partial side view of a distal end of an ablation catheter,according to other embodiments of the present invention.

FIG. 51B and an enlarged partial view of the distal end of the ablationcatheter of FIG. 51A.

FIG. 52A is a partial perspective view of the distal end of a loopcatheter, according to some embodiments of the present invention.

FIG. 52B is a side view of the loop catheter of FIG. 52A.

FIG. 52C is an end view of the loop catheter of FIG. 52A.

FIG. 53 is a side view of the distal end of an ablation catheter,according to other embodiments of the present invention.

FIGS. 54A-54C are plots of signal to noise ratio to distance for X axis,Y axis, and Z axis projections, respectively, for a four tracking coilcatheter, according to some embodiments of the present invention, andwherein each coil has two turns.

FIGS. 55A-55C are plots of signal to noise ratio to distance for X axis,Y axis, and Z axis projections, respectively, for a four tracking coilcatheter, according to some embodiments of the present invention, andwherein each coil has four turns.

FIG. 56 is a table comparing signal to noise ration for the catheters ofFIGS. 54A-54C and 55A-55C.

FIG. 57A is a partial side view of the sheath of the device of FIG. 31including multiple RF shields in end-to-end spaced-apart relationship,according to some embodiments of the present invention.

FIG. 57B is a cross-sectional view of the sheath of FIG. 57A taken alongline 57B-57B.

FIG. 57C is a cross-sectional view of the sheath of FIG. 57A taken alongline 57C-57C.

FIG. 58 is a schematic illustration of an exemplary ablation catheter,according to some embodiments of the present invention.

FIG. 59 is a schematic illustration of a self-resonant cable trap thatmay be utilized by the ablation catheter of FIG. 58, according to someembodiments of the present invention.

FIG. 60 is a cross-sectional view of a sheath with an integrated RFshield disposed therewithin for use with the ablation catheter of FIG.58, according to some embodiments of the present invention.

FIG. 61 is a partial side view of the distal end of an ablation catheterwith a portion in a sheath, such as that shown in FIG. 60.

FIG. 62A is a greatly enlarged perspective view of an RF shield disposedwithin a sheath, according to some embodiments of the present invention.

FIGS. 62B and 62C are respective opposite end views of the RF shield ofFIG. 62A.

FIG. 63 is a partial side view of a sheath including multiple RF shieldsin end-to-end spaced-apart relationship, according to some embodimentsof the present invention.

FIGS. 64-65 are graphs illustrating RF safety performance of a billabongassembly, according to some embodiments of the present invention.

FIG. 66 is a graph illustrating broad spectrum, high attenuation of abillabong assembly, according to some embodiments of the presentinvention.

FIG. 67 is a schematic illustration of a single layer billabongassembly, according to some embodiments of the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout. It will be appreciated thatalthough discussed with respect to a certain embodiment, features oroperation of one embodiment can apply to others.

In the drawings, the thickness of lines, layers, features, componentsand/or regions may be exaggerated for clarity and broken lines (such asthose shown in circuit or flow diagrams) illustrate optional features oroperations, unless specified otherwise. In addition, the sequence ofoperations (or steps) is not limited to the order presented in theclaims unless specifically indicated otherwise.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andrelevant art and should not be interpreted in an idealized or overlyformal sense unless expressly so defined herein. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

It will be understood that when a feature, such as a layer, region orsubstrate, is referred to as being “on” another feature or element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another feature or element, there are no intervening elementspresent. It will also be understood that, when a feature or element isreferred to as being “connected” or “coupled” to another feature orelement, it can be directly connected to the other element orintervening elements may be present. In contrast, when a feature orelement is referred to as being “directly connected” or “directlycoupled” to another element, there are no intervening elements present.Although described or shown with respect to one embodiment, the featuresso described or shown can apply to other embodiments.

The term “circuit” refers to an entirely software embodiment or anembodiment combining software and hardware aspects, features and/orcomponents (including, for example, at least one processor and softwareassociated therewith embedded therein and/or executable by and/or one ormore Application Specific Integrated Circuits (ASICs), forprogrammatically directing and/or performing certain described actionsor method steps). The circuit can reside in one location or multiplelocations, it may be integrated into one component or may bedistributed, e.g., it may reside entirely in an MR Scanner controlcabinet, partially in the MR Scanner control cabinet, totally in aseparate component or system such as a clinician workstation butcommunicate with MR Scanner electronics and/or in an interfacetherebetween, in a remote processor and combinations thereof.

The term “pre-set scan plane” refers to scan planes electronically(programmatically) defined for subsequent use by an MRI Scanner as beingassociated with a location of relevant anatomical tissue of a patientduring a MRI guided therapeutic or diagnostic procedure. The pre-setscan planes can be defined based on a volumetric model or map of patientanatomical structure that is subsequently registered or aligned in 3-Dimaging space and can be used to acquire near real-time MR image data ofpatient tissue. The actual pre-set scan planes are typicallyelectronically defined after the model used to select a desired spatiallocation of a corresponding relevant scan plane is registered to the 3-Dimaging space.

The term “map” is used interchangeably with the term “model” and refersto a volumetric rendering of a patient's target anatomy. The term“tissue characterization (or characteristic) map” refers to a renderedvolumetric (typically 3-D, 4-D or 4-DMP) visualization and/or image of atarget anatomical structure or portion thereof showing one or moreselected tissue parameters, conditions, or behaviors of cardiac tissueusing MR image data, e.g., the tissue characterization map is a renderedpartial or global anatomical map that shows at least one defined tissuecharacteristic of the target anatomy, e.g., heart or portion thereof(for example, the left atrium) in a manner that illustrates relativedegrees or measures of the tissue characteristic(s) of interest,typically in different colors, opacities and/or intensities. Notably, atissue characterization map or model is to be contrasted with anelectroanatomical (EA) map or model which is based on sensed electricalactivity of different regions of the heart rather than on MR image data.In some embodiments, tissue data from an electroanatomical map and/orthe tissue characteristic map can be selectively turned on and off (on adisplay) with respect to a pre-acquired model of the patient'sanatomical structure (e.g., Left Atrium). A tissue characteristic mapmay be included with an EA model and/or two or more tissuecharacteristic maps may be merged into or shown as a composite map ormay be shown overlying and aligned with one another. Thus, thevisualizations can use one or both types of volumetric tissue maps,shown separately, overlaid on each other and/or integrated as acomposite map.

The actual visualization can be shown on a screen or display so that themap of the anatomical structure is in a flat 2-D and/or in 2-D whatappears to be 3-D volumetric images with data representing features orelectrical output with different visual characteristics such as withdiffering intensity, opacity, color, texture and the like. A 4-D map caneither illustrate a 3-D anatomical structure (e.g., heart) with movement(e.g., a beating heart and/or a heart with blood flow, breathing lungsor other moving structure) or show additional information over a 3-Danatomic model of the contours of the heart or portions thereof. Theterm “heart” can include adjacent vasculature, e.g., the branching ofthe pulmonary veins.

The term “4-D multiparametric visualization” (4-DMP) means a 4-Dvisualization image (e.g., a 3-D image of a beating heart) withfunctional spatially encoded or correlated information shown on thevisualization. The 4-DMP visualization can be provided with fMRI dataand/or one or more tools used to provide the spatially correlatedfunctional data (e.g., electrical) data of the heart based on the 3-Dmodel of the tool. Again, the 3-D, 4-D and/or 4-DMP visualizations arenot merely an MRI image or MRI images of the patient during a procedurebut are rendered visualizations that can combine multiple sources ofdata to provide a visualization of spatially encoded function withanatomical shape. Thus, the visualizations can comprise a rendered modelof the patient's target anatomy with a rendered visualization of atleast one medical device in an intrabody location with respect to themodel and along with near RT MRI image data of the anatomical structure.The figures may include prophetic examples of screen shots ofvisualizations and the like and do not necessarily represent actualscreen shots of a surgical system/display.

The term “close-up” means that the associated image is shown enlargedrelative to a global image or typical navigation view to show localtissue. The term “high-resolution” means that the image data is obtainedwith higher resolution than normal image data (usually requiring longerscan times and/or using an internal antenna to increase SNR). Forexample, the local tissue ablation views may be shown in higherresolution than MRI images in the navigation view. The term en facerefers to a view through a tissue wall (e.g., myocardial wall) andsubstantially parallel (tangent) to the surface.

The term “programmatically” means that the operation or step can bedirected and/or carried out by a digital signal processor and/orcomputer program code. Similarly, the term “electronically” means thatthe step or operation can be carried out in an automated manner usingelectronic components rather than manually or using merely mental steps.

The term “target ablation path” describes a desired lesion pattern thatis selected to create a desired electrical isolation in the cardiactissue to treat the at-risk pathology/condition (e.g., AFIB). The targetablation path is not required to be followed in any particular directionor order. The path may include one or more continuous and/or contiguouslesion and/or several non-continuous or non-contiguous lesions. Thelesions may be linear (whether straight or with a curvature such ascircular or curvilinear). In any one interventional procedure, thephysician can define one or more target paths to create the desiredpattern/isolation. According to some embodiments, the target ablationpath can be used to electronically define associated physical limitsassociated with the acceptable maximum boundary limits (e.g., width,perimeter and the like) of the target ablation path.

At least a portion of an intrabody medical device is tracked and itsposition identified in 3-D imaging space (e.g., X, Y, Z coordinates),according to embodiments of the present invention. Various locationtracking means for the tool and/or registration means for the catheterto the imaging space can be employed. For example, the intrabody devicecan include fiducial markers or receive antennas combinations of same.The term “fiducial marker” refers to a marker that can be identifiedusing electronic image recognition, electronic interrogation of MRIimage data, or three-dimensional electrical signals to define a positionand/or find the feature or component in 3-D space. The fiducial markercan be provided in any suitable manner, such as, but not limited to ageometric shape of a portion of the tool, a component on or in the tool,a coating or fluid-filled coating (or combinations of different types offiducial markers) that makes the fiducial marker(s) MRI-visible that areactive or passive (e.g., if passive, the marker does not provide MRsignal) with sufficient intensity for identifying location and/ororientation information for the tool and/or components thereof in 3-Dspace. As will be discussed further below, in particular embodiments,the device comprises at least one tracking coil electrically connectedto the MRI Scanner that generates signals that are detected (received)by the MR Scanner and used to identify respective locations of the coilsin a 3-D coordinate system of the imaging space, and hence the devicewith such tracking coils, in the 3-D image space.

The terms “MRI or MR Scanner” are used interchangeably to refer to aMagnetic Resonance Imaging system and includes the magnet, the operatingcomponents, e.g., RF amplifier, gradient amplifiers and operationalcircuitry including, for example, processors (the latter of which may beheld in a control cabinet) that direct the pulse sequences, select thescan planes and obtain MR data. Embodiments of the present invention canbe utilized with any MRI Scanner including, but not limited to, GEHealthcare: Signa 1.5 T/3.0 T; Philips Medical Systems: Achieva 1.5T/3.0 T; Integra 1.5 T; Siemens: MAGNETOM Avanto; MAGNETOM Espree;MAGNETOM Symphony; MAGNETOM Trio; and MAGNETOM Verio.

The term “RF safe” means that the catheter and any (conductive) lead isconfigured to operate safely when exposed to RF signals, particularly RFsignals associated with MRI systems, without inducing unplanned currentthat inadvertently unduly heats local tissue or interferes with theplanned therapy. The term “MRI visible” means that the device isvisible, directly or indirectly, in an MRI image. The visibility may beindicated by the increased SNR of the MRI signal proximate the device.The device can act as an MRI receive antenna to collect signal fromlocal tissue and/or the device actually generates MRI signal itself,such as via suitable medical grade hydro-based coatings, fluid (e.g.,aqueous fluid) filled channels or lumens. The term “MRI compatible”means that the so-called component(s) is safe for use in an MRIenvironment and as such is typically made of a non-ferromagnetic MRIcompatible material(s) suitable to reside and/or operate in a highmagnetic field environment. The term “high-magnetic field” refers tofield strengths above about 0.5 T, typically above 1.0 T, and moretypically between about 1.5 T and 10 T. Embodiments of the invention maybe particularly suitable for 1.5 T and/or 3.0 T systems.

Generally stated, advantageously, a system according to embodiments ofthe present invention can be configured so that the surgical space isthe imaging space and the tracking is performed in the imaging space sothat there is no requirement to employ a discrete tracking system thatmust then be registered to the imaging space. In some embodiments, thetracking is carried out in the same 3-D imaging space but the flexibleintrabody medical device is tracked independent of the imaging scanplanes used to obtain the MR image data for generating images of localanatomy and is shown as a physical representation in the visualization.

The term “near real time” refers to both low latency and high framerate. Latency is generally measured as the time from when an eventoccurs to display of the event (total processing time). For tracking,the frame rate can range from between about 100 fps (frames per second)to the imaging frame rate. In some embodiments, the tracking is updatedat the imaging frame rate. For near ‘real-time’ imaging, the frame rateis typically between about 1 fps to about 20 fps, and in someembodiments, between about 3 fps to about 7 fps. For lesion imaging, anew image can be generated about every 1-7 s, depending on the sequenceused. The low latency required to be considered “near real time” isgenerally less than or equal to about 1 second. In some embodiments, thelatency for tracking information is about 0.01 s, and typically betweenabout 0.25-0.5 s when interleaved with imaging data. Thus, with respectto tracking, visualizations with the location, orientation and/orconfiguration of a known intrabody device can be updated with lowlatency between about 1 fps to about 100 fps. With respect to imaging,visualizations using near real time MR image data can be presented witha low latency, typically within between about 0.01 ms to less than about1 second, and with a frame rate that is typically between about 1-20fps. Together, the system can use the tracking signal and image signaldata to dynamically present anatomy and one or more intrabody devices inthe visualization in near real-time. In some embodiments, the trackingsignal data is obtained and the associated spatial coordinates aredetermined while the MR image data is obtained and the resultantvisualization(s) with the intrabody device (e.g., flexible catheterusing the tracking coil data) and the near RT MR image(s) is generated.

In some embodiments, MR image data is obtained during an activetreatment such as during an ablation, delivery of a drug or othermaterial, valve repair or replacement, lining repair, and the like, andthe resultant visualization(s) with the flexible intrabody device usedfor this treatment (e.g., catheter, needle and the like) along with oneor more near RT MR images of local anatomy is substantially continuouslygenerated. In some particular embodiments, the system is a cardiac EPsystem used to place a lesion pattern of transmural lesions that createsa desired electrical isolation in the cardiac tissue to treat theat-risk pathology/condition (e.g., AFIB). The ablations are not requiredto be followed in any particular direction or order. The ablation can becarried out to generate one or more continuous and/or contiguous lesionsand/or several non-continuous or non-contiguous lesions. The lesions maybe contiguous (whether straight or with a curvature such as circular orcurvilinear).

The term “intrabody device” is used broadly to refer to any diagnosticor therapeutic medical device including, for example, catheters, needles(e.g., injection, suture, and biopsy), forceps (miniature), knives orother cutting members, ablation or stimulation probes, injection orother fluid delivery cannulas, mapping or optical probes or catheters,sheaths, guidewires, fiberscopes, dilators, scissors, implant materialdelivery cannulas or barrels, and the like, typically having a size thatis between about 5 French to about 12 French, but other sizes may beappropriate.

The term “tracking member”, as used herein, includes all types ofcomponents that are visible in an MRI image including miniature RFtracking coils, passive markers, and receive antennas. In someembodiments of the present invention a miniature RF tracking coil can beconnected to a channel of an MRI Scanner. The MR Scanner can beconfigured to operate to interleave the data acquisition of the trackingcoils with the image data acquisition. The tracking data is acquired ina ‘tracking sequence block’ which takes about 10 msec (or less). In someembodiments, the tracking sequence block can be executed between eachacquisition of image data (the ‘imaging sequence block’). So thetracking coil coordinates can be updated immediately before each imageacquisition and at the same rate. The tracking sequence can give thecoordinates of all tracking coils simultaneously. So, typically, thenumber of coils used to track a device has substantially no impact onthe time required to track them.

MRI has several distinct advantages over X-ray imaging technology, suchas: excellent soft-tissue contrast, the ability to define anytomographic plane, and the absence of ionizing radiation exposure. Inaddition, MRI offers several specific advantages that make it especiallywell suited for guiding transseptal puncture procedures including: 1)near real-time interactive imaging, 2) direct visualization of criticalendocardial anatomic landmarks, 3) direct high resolution imaging of theseptum, including the fossa ovalis, 4) visualization of the needletip-tissue interface, 5) the ability to actively track needle positionin three-dimensional space, and 6) elimination of radiation exposure.

Embodiments of the present invention can be configured to guide and/orplace diagnostic or interventional devices in an MRI environment (e.g.,interventional medical suite) to any desired internal region of asubject of interest, including, in some embodiments, to a cardiaclocation. The subject can be animal and/or human subjects.

Some embodiments of the invention provide systems that can be used toablate tissue for treating cardiac arrhythmias, and/or to deliver stemcells or other cardio-rebuilding cells or products into cardiac tissue,such as a heart wall, via a minimally invasive MRI guided procedurewhile the heart is beating (i.e., not requiring a non-beating heart withthe patient on a heart-lung machine).

FIG. 1 illustrates an MRI interventional system 10 with a scanner 10Sand a flexible intrabody medical device 80 (e.g., an ablation catheter,mapping catheter, etc.) proximate target tissue 100 at a device-tissueinterface 100 i. The system 10 can be configured to electronically trackthe 3-D location of the device 80 in the body and identify and/or “know”the location of the tip portion 80 t of the device 80 (e.g., theablation tip) in a coordinate system associated with the 3-D imagingspace. As shown in FIG. 1, the device 80 can include a plurality ofspaced apart tracking members 82 on a distal end portion thereof. In aparticular embodiment, the device 80 can be an ablation catheter and thetip 80 t can include an ablation electrode 80 e (typically at least oneat a distal end portion of the device). Where used, the electrode 80 ecan be both a sensing and ablation electrode.

The tracking members 82 can comprise miniature tracking coils, passivemarkers and/or a receive antenna. In a preferred embodiment, thetracking members 82 include at least one miniature tracking coil 82 cthat is connected to a channel 10 ch of an MRI Scanner 10S (FIG. 2). TheMR Scanner 10S can be configured to operate to interleave the dataacquisition of the tracking coils 82 c with the image data acquisition.The tracking data is typically acquired in a ‘tracking sequence block’which takes about 10 msec (or less). In some embodiments, the trackingsequence block can be executed between each acquisition of image data(the latter can be referred to as an ‘imaging sequence block’). So thetracking coil coordinates can be updated immediately before each imageacquisition and at the same rate. As noted above, the tracking sequencecan give the coordinates of all tracking coils simultaneously.

Embodiments of the present invention provide a new platform that canhelp facilitate clinical decisions during an MRI-guided procedure andcan present real anatomical image data to the clinician in aninteractive visualization 100 v. The visualizations 100 v (FIGS. 5A-5D)can be dynamically generated as the intrabody device 80 moves in thebody into a target location, as a user rotates, crops or otherwisealters a displayed visualization or view and/or during an active therapyor diagnostic procedure step, e.g., while ablating at target lesionsites, with minimal latent time between serial MRI image dataacquisitions, typically less than about 5 seconds, typicallysubstantially continuously with a minimal latent time of about 1 secondor less, such as between about 0.001 seconds and 1 second. Together, thesystem 10 can use the tracking signal(s) and image signal data todynamically track the device 80 (which is typically a plurality ofdevices) and present visualizations of the anatomy and one or moreintrabody devices 80 in near real-time.

The term “physical representation” means that a device is not actuallyimaged but rather rendered with a physical form in the visualizations.The physical representation may be of any form including, for example, agraphic with at least one geometric shape, icon and/or symbol. Thephysical representation can be in 3-dimensional form. In some particularembodiments, the physical representation may be a virtual graphicsubstantial replica substantially corresponding to an actual shape andconfiguration of the physical appearance and/or configuration of atleast a portion (e.g., distal end portion) of the associated device(see, e.g., FIGS. 22A, 22B). The physical representation can beelectronically generated based on a priori knowledge of the dimensionsand configuration of the device 80. The tip and each tracking coil on adistal end of a particular device may be shown in a geometric shape (thesame or different shapes, e.g., an arrow for the tip and a sphere orblock or other (typically 3-D) shape for tracking coils, each in itsreal location in the 3-D space and in its relative position on thedevice and each may be rendered with the same or a different color. Forexample, the tip and each proximate tracking coil may be shown in adifferent color.

The term “tortuous” refers to a curvilinear pathway in the body,typically associated with a natural lumen such as vasculature. The term“dynamic visualizations” refers to a series of visualizations that showthe movement of the device(s) in the body and can show a beating heartor movement based on respiratory cycle and the like.

The term “pre-acquired” means that the data used to generate the modelor map of the actual patient anatomy was obtained prior to the start ofan active therapeutic or diagnostic procedure and can includeimmediately prior to but during the same MRI session or at an earliertime than the procedure (typically days or weeks before).

Embodiments of the present invention can be configured to guide and/orplace flexible intrabody diagnostic and/or interventional devices in anMRI environment (e.g., interventional medical suite) to any desiredinternal region of interest of a subject, typically via a natural lumenand/or tortuous path so that the intrabody devices can take on differentnon-linear configurations/shapes as it moves into position through atarget pathway (which may be a natural lumen or cavity). The subjectscan be animal and/or human subjects.

Some embodiments of the invention provide systems that can be used tofacilitate ablation of tissue for treating cardiac arrhythmias, or torepair or replace cardiac valves, repair, flush or clean vasculatureand/or place stents, and/or to deliver stem cells or othercardio-rebuilding cells or products into cardiac tissue, such as a heartwall, via a minimally invasive MRI guided procedure while the heart isbeating (i.e., not requiring a non-beating heart with the patient on aheart-lung machine). The cardiac procedures can be carried out from aninside of the heart or from an outside of the heart. The system may alsobe suitable for delivering a therapeutic agent or carrying out anothertreatment or diagnostic evaluation for any intrabody location,including, for example, the brain, gastrointestinal system, genourinarysystem, spine (central canal, the subarachnoid space or other region),vasculature or other intrabody locations. Additional discussion ofexemplary target regions can be found at the end of this document.

The system 10 and/or circuit 60 c (FIGS. 2-3) can calculate the positionof the tip of the device 80 t as well as the shape and orientation ofthe flexible device based on a priori information on the dimensions andbehavior of the device 80 (e.g., for a steerable device, the amount ofcurvature expected when a certain pull wire extension or retractionexists, distance to tip from different coils 82 and the like). Using theknown information of the device 80 and because the tracking signals arespatially associated with the same X, Y, Z coordinate system as the MRimage data, the circuit 60 c can rapidly generate visualizations showinga physical representation of the location of a distal end portion of thedevice 80 with near RT MR images of the anatomy.

In some embodiments, the tracking signal data is obtained and theassociated spatial coordinates are determined while a circuit 60 c inthe MRI Scanner 10S (FIG. 2) and/or in communication with the Scanner10S (FIG. 3) obtains MR image data. The reverse operation can also beused. The circuit 60 c can then rapidly render the resultantvisualization(s) 100 v (see, e.g., FIGS. 5A-5D) with the flexibledevice(s) 80 shown with a physical representation based on spatialcoordinates of the devices in the 3-D imaging space identified using theassociated tracking coil data and the near RT MR image(s).

The circuit 60 c can be totally integrated into the MR Scanner 10S(e.g., control cabinet), partially integrated into the MR Scanner 10S orbe separate from the MR Scanner 10S but communicate therewith. If nottotally integrated into the MR Scanner 10S, the circuit 60 c may residepartially or totally in a workstation 60 and/or in remote or other localprocessor(s) and/or ASIC. FIG. 3 illustrates that a clinicianworkstation 60 can communicate with the MR Scanner 10S via an interface44. Similarly, the device 80 in the magnet room can connect to the MRScanner 10S via an interface box 86 which may optionally be integratedinto the patch panel 250.

As shown in FIGS. 2 and 3, for example, the system 10 can include atleast one (interactive) display 20 in communication with the circuit 60c and/or the Scanner 10S. The display 20 can be configured to displaythe interactive visualizations 100 v. The visualizations 100 v can bedynamic showing the movement of the device 80 relative to the intrabodyanatomical structure shown by the displayed near-real time MRI image.

The system 10 can include a User Interface (UI) 25 with several UIcontrols 25 c (FIG. 7), such as a graphic UI (GUI), in communicationwith the display 20 and may be configured to allow a user to select toshow one or more pre-acquired or in situ generated maps and/or images 30of target tissue including different tissue characterization maps and/oran optional EA map (or data from those maps) which can be shown inand/or with the visualization 100 v. For example, the system 10 can beconfigured to allow a user to select to show a map of patientvasculature and/or fibrous tissue based on pre-acquired image data (suchas segmented MRA (Magnetic Resonance Angiography or other image slices)with the map or data therefrom being registered to and overlaid onto orincorporated into at least one of the models 100M in the visualizationand can be selectively turned on and off by a user. This information mayhelp a clinician select a treatment site or avoid a treatment site orotherwise affect clinical choices. For example, for cardiac use, ifvasculature with a relatively large blood flow is shown in a targetlesion space in cardiac tissue and/or if fibrous tissue is shown, aclinician may choose another spot or may ablate longer to form atransmural lesion. Further examples of display options will be discussedfurther below.

In some embodiments, the system/circuit can employ interactiveapplication of non-selective saturation to show the presence of acontrast agent in near real-time scanning. This option can help, forexample, during image-guided catheter navigation to target tissue thatborders scar regions. See, e.g., Dick et al., Real Time MRI enablestargeted injection of labeled stem cells to the border of recent porcinemyocardial infarction based on functional and tissue characteristics,Proc. Intl. Soc. Mag. Reson. Med. 11, p. 365 (2003); Guttman et al.,Imaging of Myocardial Infarction for Diagnosis and Intervention UsingReal-Time Interactive MRI Without ECG-Gating or Breath-Holding, Mag.Reson. Med, 52: 354-361 (2004), and Dick and Guttman et al., MagneticResonance Fluoroscopy Allows Targeted Delivery of Mesenchymal Stem Cellsto Infarct Borders in Swine, Circulation, 2003; 108:2899-2904, whichdescribe, inter alia, imaging techniques used to show regions of delayedenhancement in (near) real-time scans. The contents of these documentsare hereby incorporated by reference as if recited in full herein.

FIG. 2 illustrates that the device 80 can include at least one conductor81, such as a coaxial cable that connects a respective tracking coil 82c to a channel 10 ch of the MR Scanner 10S. The MR Scanner 10S caninclude at least 16 separate channels, and typically more channels butmay operate with less as well. Each device 80 can include between about1-10 tracking coils, typically between about 1-4. The coils 82 c on aparticular device 80 can be arranged with different numbers of turns,different dimensional spacing between adjacent coils 82 c (where morethan one coil is used) and/or other configurations. The circuit 60 c canbe configured to generate the device renderings based on tracking coillocations/positions relative to one another on a known device with aknown shape and/or geometry or predictable or known changeable(deflectable) shape or form (e.g., deflectable end portion). The circuitcan identify or calculate the actual shape and orientation of the devicefor the renderings based on data from a CAD (computer aided design)model of the physical device. The circuit can include data regardingknown or predictable shape behavior based on forces applied to thedevice by the body or by internal or external components and/or based onthe positions of the different tracking coils in 3-D image space andknown relative (dimensional) spacings.

As shown in FIG. 3, the display 20 can be provided in or associated witha clinician workstation 60 in communication with an MRI Scanner 10S.Other displays may be provided. The MRI Scanner 10S typically includes amagnet 15 in a shielded room and a control cabinet 11 (and othercomponents) in a control room in communication with electronics in themagnet room. The MRI Scanner 10S can be any MRI Scanner as is well knownto those of skill in the art.

The tracking coils 82 c can each include a tuning circuit that can helpstabilize the tracking signal for faster system identification ofspatial coordinates. FIG. 4 illustrates an example of a tuning circuit83 that may be particularly suitable for a tracking coil 82 c. As shown,CON1 connects the coaxial cable 81 to the tracking coil 82 c on a distalend portion of the device 80 while J1 connects to the MR Scanner channel10 ch. The Scanner 10S sends a DC bias to the circuit 83 and turns U1diode “ON” to create an electrical short which creates a high impedance(open circuit) on the tracking coil to prevent current flow on thetracking coil and/or better tracking signal (stability). The tuningcircuit can be configured to have a 50 Ohm matching circuit (narrow bandto Scanner frequency) to electrically connect the cable to therespective MR Scanner channel. When the diode U1 is open, the trackingcoil data can be transmitted to the MR Scanner receiver channel 10 ch.The C1 and C2 capacitors are large DC blocking capacitors. C4 isoptional but can allow for fine tuning (typically between about 2-12picofarads) to account for variability (tolerance) in components. It iscontemplated that other tuning circuits and/or tracking signalstabilizer configurations can be used. The tuning circuit 83 can residein the intrabody device 80 (such as in a handle (e.g., 440, FIG. 31) orother external portion), in a connector that connects the coil 82 c tothe respective MRI scanner channel 10 ch, in the Scanner 10S, in aninterface box 86 (FIG. 2), a patch panel 250 and/or the circuit 83 canbe distributed among two or more of these or other components.

In some embodiments, each tracking coil 82 c can be connected to acoaxial cable 81 having a length to the diode via a proximal circuitboard (which can hold the tuning circuit and/or a decoupling/matchingcircuit) sufficient to define a defined odd harmonic/multiple of aquarter wavelength at the operational frequency of the MRI Scanner 10S,e.g., λ/4, 3λ/4, 5λ/4, 7λ/4 at about 123.3 MHz for a 3.0 T MRI Scanner.This length may also help stabilize the tracking signal for more preciseand speedy localization. The tuned RF coils can provide stable trackingsignals for precise localization, typically within about 1 mm or less.Where a plurality (e.g., two closely spaced) of adjacent tracking coilsare fixed on a substantially rigid material, the tuned RF tracking coilscan provide a substantially constant spatial difference with respect tothe corresponding tracking position signals.

The tracking sequence used in the system 10 can intentionally dephasesignal perpendicular to the read-out direction to attenuate unwantedsignal from 1) bulk objects and 2) regions sensed by other signalsensitive parts of the catheter which couple to the tracking coil (e.g.the coaxial cable along the catheter shaft). This tends to leave only asharp peak indicating the position of the tracking coil.

The tracking sequence block can include or consist of a plurality of(typically about three) repetitions of a small flip-angle excitation.Each repetition is designed to indicate the x, y or z component of thetracking coil coordinates in succession. Frequency encoding is usedalong the x-direction to obtain the x-coordinate, the y-direction forthe y-coordinate, and the z-direction for the z-coordinate. When thefrequency encoding is in the x-direction, the other two directions (yand z) are not spatially encoded, producing projection (spatiallyintegrated) signals in those directions from all excitation regions. Thedephasing gradient attempts to attenuate unwanted signal included inthese projections. Once the tracking sequence block is complete, aspoiler gradient can be used to dephase any transverse signal remainingfrom the tracking before the imaging sequence block is executed.

The imaging sequence block obtains a portion, depending on theacceleration rate, of the data used to reconstruct an image of a singleslice. If the acceleration rate is 1, then all of the data for an imageis collected. If the acceleration rate is 2, then half is collected,etc. If multiple slices are activated, then each successive imagingblock collects data for the next slice, in ‘round robin’ fashion. If anymagnetization preparation (e.g., saturation pulses) is activated, theseare executed after the tracking sequence block, immediately before theimaging sequence block.

Additional discussion of tracking means and ablation catheters can befound in U.S. Pat. No. 6,701,176, and U.S. Provisional Application Ser.No. 61/261,103, the contents of which are hereby incorporated byreference as if recited in full herein. Exemplary catheters will bediscussed further below.

Referring now to FIGS. 5A-5D and 6, examples of visualizations 100 vwith a physical representation 80R of the intrabody device 80, avolumetric model 100M of target anatomical structure and a nearreal-time MRI image 100MRI. The circuit 60 c/Scanner 10S is configuredto present a 3-D volumetric model of at least a portion of the patient'starget anatomy (shown as the heart) 100M in the visualization 100 v withthe model registered to the 3-D imaging space along with a physicalrepresentation of at least the distal end portion of the at least oneintrabody device 80R in the imaging space. Optionally, thevisualizations can be carried out to show the tracking coils in thephysical representation of the distal end portion of the medical devicein different colors using the identified location of the tracking coilsand defined form factor and/or dimensional data regarding actual coilplacement on the device.

The circuit 60 c can be configured to generate the visualizations 100 vwith at least two visual reference planes 41, 42 (shown with a thirdintersecting plane 43) that are typically oblique or orthogonal to eachother and extend through at least a major portion of the visualization100 v. The planes 41, 42 (and 43) can be transparent and/or translucent.They may be shown with different color perimeters that correspond to arespective two-dimensional image slice (which may be shown as thumbnailson the display also with a perimeter of similar or the same color).

The planes 41, 42 can move relative to each other in the imaging spaceor may be locked together, in any case they can be configured to moverelative to the model 100M in the imaging space. As shown in FIGS.5A-5D, a user can rotate and zoom the visualization 100 v whichautomatically adjusts the visualization shown on the display. As alsoshown, the flexible device 80 is not required to be in any of therelevant anatomical scan planes used to obtain MR data for the at leastone near RT MRI image 100MRI in the visualization and the distal endportion 80 d of the flexible device 80 can take on a curvilinear shapeand the tip 80 t can be steered or guided into different targetpositions.

In some embodiments, as shown in FIG. 5D, the circuit 60 c is configuredto associate a tip location of the at least one device 80 with an arrow82 a or other visual feature and render the visualization so that eachtracking coil 82 on the distal end portion 80 d has a shape 82 s with acolor, with each tracking coil 82 having a respective different colorfrom the other tracking coils, and with a line or spline 82/connectingthe tip 82 a and the coils 82 c and the line 82/is able to flex, bendand move to reflect movement of the device 80 in the visualizations 100v. The system/circuit can be configured to display color-highlightedimages generated using tracking coil data from the MR Scanner trackingcoil channels so as to display the coils as color high-lighted featuresin the 3D rendering of the physical representation of the device (e.g.,catheter).

FIG. 6 illustrates that the system 10 can be configured to show both theinteractive visualization 100 v in one viewing window 20 w ₁ and an MRIimage 100MRI alone in a second viewing window 20 w ₂. The MRI image100MRI in the second window 20 w ₂ is typically associated with thetarget anatomy location (identified by a user) in the interactivevisualization 100 v in the first viewing window 20 w ₁.

As shown in FIG. 7, the display 20 can have a UI 25 with at least one UIcontrol 25 c configured to allow a physician or other clinician toselect whether to show near real time MR images of target tissue 100MRIeither with a model 100M of the target anatomical structure (FIG. 7)and/or in a separate viewing window (FIGS. 6, 13-16). The circuit 60 isin communication with at least one display 20 with the UI 25.

The UI 25 can be configured to allow a user to alter the displayedvisualization (fade) to include only a near RT image of the anatomy, toinclude the near RT image of the anatomy and the registered model of theheart, or to include only the registered model, see, for example, FIG. 7showing both types of images in the visualization 100 v with FIG. 9which shows only the model 100M. The UI 25 can be an on off selection ofthese options or may “fade” from one viewing option to another. Asshown, a virtual sliding control 25 c allows a user to change what isshown ((near) RTMRI 100MRI to only the Model 100M).

The circuit 60 c can also be configured to generate images showing thedevice location in MR image space. The UI 25 can also be configured toallow a user to fade the renderings of the device 80 in and out of thevisualizations with actual images of the device and tracking coils toconfirm location or for additional visual input. The device may includeother fiducial markers (e.g., a passive marker or an active marker suchas receive antenna) for facilitating the visual recognition in the MRimage.

The UI 25 typically includes multiple GUI controls 25 c that can includea touch screen input control to allow a clinician/physician to select aregion of interest in the map 100M by placing a cursor or by touchingthe screen at a region of interest. This can cause the system to obtainreal time MR image data of that region and provide the associated imageon the display and/or define scan planes (which may be preset scanplanes) at that location in space.

Referring again to FIG. 7, for example, the display 20 can be incommunication with a UI 25 that provides a plurality of user selectabledifferent maps 30 so that the map or data therefrom can be “turned onand off” on the displayed 3-D anatomical map registered to the imagingspace. The different maps can comprise a patient-specific 3-D(volumetric) anatomical map, and/or data that can be shown on the 3-Danatomical map, registered to the imaging space. For tissuecharacterization maps, the maps include spatially correlated tissuecharacterization data taken from MR image data incorporated therein asdiscussed above. The UI 25 can include multiple different GUI controls25 c for different functions and/or actions. The GUI controls 25 c mayalso be a toggle, a touch screen with direction sensitivity to pull inone direction or other graphic or physical inputs.

The user selectable patient-specific maps 30 including a plurality oftissue maps, typically including at least one, and more typicallyseveral types of, tissue characterization maps (or data associated withsuch maps to be shown on a registered model) associated with theprocedure that can be selected for viewing by a user. The UI 25 can alsoinclude GUI controls that allow a user to select two or more of thetissue characteristic maps, with such data able to be shown together(overlaid and registered and/or as a composite image/map) or separately.As shown, the maps 30 and/or data therefrom, may include at least aplurality of the following user selectable data:

(a) a regional evaluation scan map 32 r (FIG. 17) and/or a globalevaluation scan map 32 g (FIG. 13) which shows tissue information, e.g.,actual lesion patterns in one region to allow a clinician to viewregional ablation information (such as at the LA (left atrium), a PV(pulmonary vein) and the like);

(b) pre-procedure MRI cardiac scans 34 (FIG. 7);

(c) DHE 1 (Delayed Hyper Enhancement) tissue characterization map 35 ataken at a first point in time (such as a week or just prior to theprocedure) (FIG. 28);

(d) DHE 2 tissue characterization map 35 b taken at a second point intime, such as during a procedure, potentially toward an end of theprocedure (for cardiac ablation procedures that can be used to confirmcomplete electrical isolation of the PV (pulmonary veins) or othertargets prior to terminating the procedure—alternatively the DHE 2 mapcan be associated with the end of a prior EP ablation procedure) (FIG.27);

(e) an EA (electroanatomical) map 35 c (FIG. 17);

(f) an edema tissue characterization map 35 d (FIG. 19);

(g) other tissue characterization maps 35 e, for example:

-   -   (i) a composite thermal tissue characterization map that shows        positions of increased temperature that were caused by ablation        of tissue during the procedure;    -   (ii) ischemic (oxygen deprived or lacking) tissue        characterization map;    -   (iii) hypoxic or necrotic tissue characterization map;    -   (iv) fibrous tissue map;    -   (v) vasculature map;    -   (vi) cancer cell/tissue map (where cancer is the condition being        treated);

(h) at least one procedure planning map 37M with target sites 37 p (alsoreferred to interchangeably herein as sites 55 t) and a later tissue mapshowing actual sites 37 a (e.g., target and actual ablation sites) shownin different colors, opacities and/or intensities for ease of reference(see, e.g., FIG. 10, red/darker spots associated with target and greenor lighter spots associated with actual); and

(i) device views 36 that show the physical representation of the device80 in the surgical/imaging space, e.g., with an ablation catheter 36 ashown in position and/or a mapping (loop) catheter 36 b as devices 80shown in position (FIGS. 9, 11). These device maps 36 may beused/displayed, for example, during a navigation mode. The defaultaction may be to show these devices at least in the navigation mode buta user can deselect this choice.

The tissue maps 30 (or tissue characterization data) are typicallyregistered to the 3-D coordinate image space (manually or via automaticelectronic image alignment registration means). In some embodiments,relevant image scan planes and MR image data of the patient can beimported and/or incorporated into one or more of the tissuecharacterization maps so that the map(s) can be updated over time(including in real time) using MR image data correlated with theanatomical location on the tissue characterization map and shown on the(updated) tissue characterization map 30 automatically or upon requestby a user. EA maps can be generated using tracking and/or mappingcatheters in MRI images space which may provide a more accurate ortimely EA map.

The tissue map(s) 30 can be generated using MR image data that showsnormal and abnormal status, conditions and/or behavior of tissue. Forexample, the tissue characterization map(s) can show a thermal profilein different colors (or gray scale) of cardiac tissue in a region ofinterest and/or globally. In other embodiments, the tissuecharacterization map can illustrate one or more of infarct tissue, otherinjured tissue such as necrotic or scar tissue, hypoxic, ischemic,edemic (e.g., having edema) and/or fibrotic tissue or otherwiseimpaired, degraded or abnormal tissue as well as normal tissue on ananatomical model of the heart. In yet other embodiments, the tissuecharacterization map can illustrate portions of the heart (e.g., LA orposterior wall) with lesser or greater wall motion, and the like.

Whether a parameter or tissue characteristic is shown in a respectivetissue characterization map 30 as being impaired, degraded or otherwiseabnormal versus normal can be based on the intensity of pixels of thetissue characteristic in the patient itself or based on predefinedvalues or ranges of values associated with a population “norm” oftypical normal and/or abnormal values, or combinations of the above.

Thus, for example, normal wall motion can be identified based on, acomparison to defined population norms and different deviations fromthat normal wall motion can be shown as severe, moderate or minimal indifferent colors relative to tissue with normal wall motion.

In another example, a thermal tissue characterization map 30 canillustrate tissue having increased temperatures relative to otheradjacent or non-adjacent tissue. Thus, for example, during or shortlyafter ablation, the lesioned tissue and tissue proximate thereto canhave increased temperatures relative to the non-lesioned temperature ortissue at normal body temperatures. Areas or volumes with increasedintensity and/or intensity levels above a defined level can beidentified as tissue that has been ablated. The different ablation sites55 t can be shown on the map 30 as areas with increased temperatures(obtained at different times during the procedure) and incorporated intothe thermal tissue characterization map 30 automatically and/or shownupon request.

In some embodiments, the tissue characteristic map 30 uses MR image dataacquired in association with the uptake and retention of a (e.g., T-1shortening) contrast agent. Typically, a longer retention in tissue isassociated with unhealthy tissue (such as infarct tissue, necrotictissue, scarred tissue and the like) and is visually detectable by adifference in image intensity in the MR image data, e.g., using a T1weighted sequence, to show the difference in retention of one or morecontrast agents. This is referred to as delayed enhancement (DE),delayed hyper-enhancement (DHE) or late gadolinium enhancement (LGE). Asdiscussed above, in some embodiments, the system/circuit can employinteractive application of non-selective saturation to show the presenceof a contrast agent in near real-time scanning. This option can help,for example, during image-guided catheter navigation to target tissuethat borders scar regions. Thus, the DHE image data in a DHE tissuecharacterization map can be pre-acquired and/or may include near-RTimage data.

The tissue map is typically a volumetric, 3-D or 4-D anatomical map thatillustrates or shows tissue characterization properties associated withthe volume as discussed above. The map can be in color and color-codedto provide an easy to understand map or image with different tissuecharacterizations shown in different colors and/or with differentdegrees of a particular characterization shown in gray scale or colorcoded. The term “color-coded”means that certain features or conditionsare shown with colors of different color, hue or opacity and/orintensity to visually accentuate different conditions or status oftissue or different and similar tissue, such as, for example to showlesions in tissue versus normal or non-lesion tissue.

In some embodiments, the UI 25 can be configured to allow a clinician toincrease or decrease the intensity or change a color of certain tissuecharacterization types, e.g., to show lesion tissue or tissue havingedema with a different viewing parameter, e.g., in high-contrast colorand/or intensity, darker opacity or the like. A treatment site, such asa lesion site(s) in/on the tissue characterization map 30 can be definedbased on a position in three-dimensional space (e.g., where an electrodeis located based on location detectors, such as tracking coils, when theablation electrode is activated to ablate), but is typically also oralternately associated with MRI image data in associated scan planes toshow an ablation site(s) in an MRI image. The MR image data may alsoreflect a change in a tissue property after or during ablation duringthe procedure, e.g., DHE, thermal, edema and the like.

The circuit 60 c can be configured to generate a tissue map 37M (FIG.27) that is a difference or a comparison map that is generated from apre-procedure or start-of procedure tissue data and an intra-proceduretissue data to show the differences based on the procedure. The “before”and “after” maps can be electronically overlaid on a display and shownin different colors, opacities and/or intensities or corresponding pixelvalues from each image in a region of interest (ROI) can be subtractedto show a difference map or otherwise integrated into a composite map.Again, the UI 25 can allow a clinician to select or deselect (or togglebetween) the before or after tissue characterization maps or adjustdisplay preferences to allow a visual review of differences.

A regional update tissue map 32 can be used to evaluate whether targetor actual treatment sites have been successfully treated, e.g., whetherablated locations have the desired transmural lesion formation. Forexample, the UI 25 can allow the clinician to select a high resolutionor enlarged view of the actual ablated tissue merely by indicating onthe interactive map 100M, such as a regional evaluation tissue map, adesired region of interest (e.g., by pointing a finger, cursor orotherwise selecting a spot on the display). For example, a highresolution MR image of suspect tissue in the LSPV can be shown so thatthe physician can see actual tissue in the desired spot indicated on thetissue characterization map. New targets can be electronically marked onthe map as needed and scan planes can be automatically electronically beselected, identified or otherwise associated with the new targetlocation.

FIG. 13 shows the display 20 with side-by-side viewing windows, onewindow showing the visualization with the map 100M (which may be atissue characterization map) and the other window with at least one nearRT MRI image of local tissue during an active treatment mode.

FIGS. 22A and 22B illustrate two windows of the axial and en face viewsof local tissue. FIG. 22A shows the tissue prior to ablation and FIG.22B shows the tissue during or after an ablation. For example, during anablation mode the system can use a default viewing rule to display thenear real time MR image data of the affected tissue during thetreatment, e.g., ablation, typically showing both en face and side viewsof the local tissue and treatment (ablation tip) according toembodiments of the present invention. In certain embodiments, theinteractive visualization map 100 v and/or model 100M may not bedisplayed during all or some of the ablation.

Referring to FIGS. 8, 12, and 25, in some embodiments, the UI 25 canalso include a user input control 25 c to allow a user to identifyand/or select (e.g., mark) target ablation sites 55 t on a tissueplanning map 37M and subsequently provide planned and actual ablationtissue maps 37 a or (which may be overlaid with different colors foreasy comparison in viewing) or merged into a composite map thatindicates both planned and actual sites (FIG. 10).

FIGS. 14, 17 and 22A-22B illustrate enlarged (high resolution image)views of tissue that can be shown based on actual MR image data. Thisallows a physician to see the tissue that is targeted for treatment(e.g., ablation) prior to and/or during treatment (e.g., ablation). Thistype of viewing can be carried out during a planning stage or toevaluate lesions after ablation rather than just during the treatmentfor tissue-specific data. In some embodiments, the enlarged image viewscan be shown in response to user input in the interactive visualization.That is, the image views can be based on the placement of a targettreatment site 55 t in or on the map 100M.

FIG. 14 illustrates that a clinician (physician) can mark an area on themodel 100M of the interactive visualization 100 v shown as a circletoward the left side of the left window. FIG. 15 shows that the lesionpattern may be incomplete. FIG. 16 illustrates that the marked area inFIG. 14 may define the scan plane for the close-up views in the righthand viewing window.

FIGS. 10, 12 and 13 illustrate a “complete” planning map 37M with anumber of target ablation sites 37 p/55 t for forming desired transmurallesions and/or electrical isolation patterns as selected by thephysician (user). FIG. 10 illustrates both planned and actual treatmentsites. After a planned ablation pattern is indicated, or as a mark orparticular lesion site is selected and/or placed on the planning map37M, a physician/user can review real-time MR image data of the spot andaffirm the selected site is a desired target ablation site(s) 55 t. FIG.8 illustrates that the display can show a planned ablation site pattern55 t applied to the model 100M along with near real time patient MRIdata.

In some embodiments, the planned treatment (e.g., ablation) pattern canuse an electronically generated (default) template based on a predefinedcondition to be treated and certain fiducials associated with the targetanatomy. The template may also be based on a clinician-specificpreference for such a condition that can be electronically stored foruse over different patients. The template can be modified based onpatient-specific anatomy or other information. The ablation pattern canbe electronically “drawn” or marked on the model 100M prior to itsregistration in the image space. The system can be configured toelectronically identify relevant scan planes for the different markedlesion sites or areas after registration in the image space or proposescan planes that match contour of local anatomy that will include thetarget ablation site(s).

FIG. 17 illustrates that the display can show the interactivevisualization 100 v in one viewing window and that previous ablations inthe indicated region can have an electronic associated scan plane(s)that can be used to define a new (or current) scan plane for regionalevaluation of the lesion or other therapy.

FIG. 20 shows that the visualization 100 v can be used to confirm adesired therapy plan (ablation sites) and set a regional scan plane.Note also the difference from FIG. 8 with the visualization showing themodel more predominant than the MR image data according to user input.

The model/map 100M can be shown in wire grid form (FIG. 9) or in varyingintensity or opacity based on user input or default settings. FIG. 9also shows the near RT image data suppressed or not shown in thevisualization 100 v.

FIG. 22A shows that scan planes for the therapeutic (e.g., ablation)view(s) can be automatically determined based on the identified locationof the tracking coil(s) 82 c as discussed above.

The circuit 60 c can electronically define and pre-set scan planesassociated with a respective target ablation site correlated to anactual location in 3-D space which is then electronically stored inelectronic memory as pre-set scan planes for that target location. TheMRI images in treatment-view mode (e.g., ablation-view mode) canautomatically be displayed when the treatment device 80 reaches thecorresponding physical location in the target anatomy (e.g., heart)during the procedure. The planned target sites 55 t may also used todefine the physician view (3-D perspective), e.g., a preset view,whenever the treatment device 80 (e.g., ablation catheter) is inproximity to the defined location associated with the target site. Thus,the target sites 55 t identified in the planning map 37M can be used topreset both associated scan planes with real time MRI and the 3-D viewfor display without requiring further clinician input.

During the procedure, as the distal end 80 t of the device 80 (e.g.,ablation catheter) approaches a location that corresponds to a targettreatment (e.g., ablation) site 55 t, the circuit 60 c (e.g., MR Scanner10S) can automatically select scan planes that “snap to” the tiplocation using a scan plane defined “on the fly” based on the locationof the end of the device (typically selected so that the slice includesa region projected forward a distance beyond the tip of the device suchas between about 0-4 mm, typically about 1-2 mm) and/or using one ormore of the preset scan planes associated with that location to obtainreal-time MR image data of the associated tissue. The scan planes can beadjusted in response to movement of the device (as typically detected bytracking coils) prior to or during treatment. FIG. 11 indicates anauto-view using a recalled preset scan plane as the device 80 nears orcontacts target tissue.

For example, in some embodiments, the circuit 60 c and/or MR Scanner 10Scan adjust the scan planes if the physician moves the ablation catheterto obtain slices that show the ablation of the lesion including side anden face views showing substantially real-time MRI of the tissue beingablated. The scan planes are selected to include slices that areprojected outward a distance axially along the line of the device toinclude relevant tissue.

In addition to substantially continuous collection of “new” image datain the visualizations and/or ablation or other therapy view modes, thedata can also be processed by algorithms and other means in order togenerate and present back to the surgeon in near real-time or uponrequest, a continuously updated, patient specific anatomical tissuecharacterization map of the anatomy of interest.

FIG. 23 illustrates that the system can illustrate the location of thetreatment device 80 with additional visual indicators and a “target”mark for help in navigation to the site.

FIGS. 24A-24D illustrate that the system can generate visualnavigational markers for facilitating alignment using MRI-guidance.

In particular embodiments, during ablation, MR thermometry (2-D) can beused to show real-time ablation formation taking a slice along thecatheter and showing the temperature profile increasing. It iscontemplated that 2D and/or 3D GRE pulse sequences can be used to obtainthe MR image data. However, other pulse sequences may also be used.

FIGS. 18 and 19 illustrate examples of maps 30 of pre-acquired patientdata that can be imported (and registered to the image space) for useduring a cardiac interventional procedure, typically used as the map100M in the interactive visualization 100 v. As shown in FIG. 18, an EAmap can be obtained prior to (typically immediately prior to) the actualinterventional procedure either while the patient is in the MRI scanneror from an X-ray based system from which the EA map can be registered toa different map, such as a tissue characterization map 30 and shown onthe display 20. In some embodiments, the tissue characterization map caninclude, incorporate, overlay or underlay data from or an EA map (whichmay be imported from an X-ray imaging modality or generated in an MRIScanner) to define an integrated electro and tissue characterizationcombination map. The electrical activity can be detected via electricalactivity sensors that can detect impedance or other electrical parameterthat can sense fractionated or normal electrical activity in cardiactissue as is known to those of skill in the art. The electroanatomicalmap or data therefrom, where used, can be registered to thevisualization map 100M (e.g., a different tissue-characterization map)so that MR data updates using MR data that is generated during theintervention can be generated and displayed on the integrated map.

Also, the UI 25 can be configured to allow a clinician to select ordeselect the EA map (where used) so that the information from the EA mapis electronically stripped or removed (and/or added back in) to the map100M as desired. In other embodiments, the map 100M is maintainedseparate from the EA map, and if used, the EA map is shown in a separatewindow or screen apart from the tissue characterization map.

FIGS. 21 and 27 show examples of MRI DHE tissue characterization maps.FIG. 21 shows a pre-procedure “planning” DHE image taken before,typically about 1 week before, the planned procedure. In someembodiments, a DHE image can be taken after a prior ablation procedureillustrating locations of incomplete electrical isolation/scar formationfor helping plan the target sites for the current procedure. A planningmap can be placed over the map in the visualization so that auser/physician can mark the target ablation sites 55 t as discussedabove (which may in some embodiments also define preset scan planes andviews before ablating during a procedure). FIG. 27 shows anintraprocedure DHE map that can be used to evaluate the ablation sites.

FIG. 28 illustrates that the map 100M can be rendered to show locationsof target and actual ablation sites (in different colors) to allow aclinician to evaluate the scar formations and/or variation from theplanned procedure intra-procedure according to embodiments of thepresent invention.

The MRI Scanner 10S (FIGS. 1-3) can be operated substantiallycontinuously to provide image data that can be used to generate updatedmaps 100M in the visualizations upon request or automatically. Thisoperation can be “in the background”, e.g., transparent to the user soas not to slow down the procedure while providing updated image andtracking data during the course of the procedure.

In some embodiments, the device-tissue interface 100 i (FIG. 1, 22A,22B) can be visualized with a T1-weighted FLASH sequence (T1w FLASH) tolocalize the tip 80 t. RF or other ablative energy can be delivered andmyocardial or other target tissue changes and lesion formation can bevisualized in near real-time using a T2 weighted HASTE (T2w HASTE)sequence. Real Time (RT)-MRI sequence, T1w FLASH and T2w HASTE imageslices can be aligned to allow visualization of the device 80 upontissue contact or activation of the ablation energy to allowvisualization of the device 80 (e.g., catheter), the device-tissueinterface 100 i and/or the (myocardium) tissue while receiving thetherapy, e.g., ablative energy.

In some particular embodiments, during navigation mode (rather than anablation mode), the catheter 80 can be visualized using a differentpulse sequence from that used in the high-resolution ablation mode, suchas, for example, an RT MRI sequence using GRE or SSFP (e.g., TrueFISP)pulse sequence with about 5.5 fps), the tracking coils 82 c can be usedfor spatial orientation and positioning. Typical scan parameters for(near) real-time include: echo time (TE) 1.5 ms, repetition time (TR)3.5 ms, a flip angle of about 45 degrees or about 12 degrees, slicethickness 5 mm, resolution 1.8 mm×2.4 mm, parallel imaging withreduction factor (R) of 2. In some embodiments using SSFP, the flipangle is about 45 degrees.

Once the device position is deemed appropriate (using tracking coils 82c), a pulse sequence at the associated scan plane can be used togenerate high resolution visualization of the catheter tip 80 t and(myocardial) tissue interface. For example, a T1-weighted 3D FLASHsequence (T1w FLASH) as noted above. Myocardial or other target tissueimages during ablation or other therapy can be acquired using an InnerVolume Acquisition (IVA) dark-blood prepared T2-weighted HASTE (T2wHASTE) or dark-blood prepared Turbo Spin Echo (TSE) sequence. Examplesof HASTE and TSE sequence parameters include: TE=79 ms/65 ms, TR=3 heartbeats, 3 contiguous slices with thickness of about 4 mm, resolution 1.25mm×1.78 mm/1.25 mm×1.25 mm, fat saturation using SPAIR method, andparallel imaging with R=2, respectively.

Typical heart beat rates and free breathing can present imagingchallenges. In some embodiments, (near) RT navigation imaging slices(e.g., GRE pulse sequence at 5.5 fps) can be aligned withhigh-resolution tissue interface slices (e.g., T1w FLASH) forvisualization of the catheter-tissue interface. Subsequently, thoseslices obtained with T1w FLASH can be aligned with those obtained withdark-blood prepared T2w Haste images for myocardial tissue/injurycharacterization during energy delivery. This stepwise approach canallow confident localization of specific points within the atrium andwhile ablating tissue and simultaneously visualizing the tissue fornear-real time assessment of tissue injury associated with lesionformation.

In some embodiments, slices acquired with different sequences can beinterlaced to provide an interactive environment for cathetervisualization and lesion delivery, a UI can allow a user to togglebetween these views or can alternate the views based on these imageslices or navigation versus ablation or interventional modes/views. Itis also noted that the sequences described herein are provided asexamples of suitable sequences and it is contemplated that other knownsequences or newly developed sequences may be used for cardiac ablationor other anatomy or interventional procedures.

FIG. 29 illustrates one particular embodiments using a cardiac MRIInterventional suite 19 with an integrated cable management system thatconnects multiple patient connected leads that remain in position evenwhen a patient is translated in or out of a magnet bore on the gantry 16(the magnet can be an open face or closed magnet configuration) to allowa clinician direct access to a patient. The other ends of the leadsconnect to power sources, monitors and/or controls located remote fromthe patient (typically in the control room not the magnet room). Asshown in FIG. 29, the MRI interventional suite 19 can include an IV pole140 (typically attached to the scanner table/gantry 16) and a connectionblock 150 of cables 200 n that are routed through a ceiling (e.g., theyextend up, through and above a ceiling) (where “n” is typically betweenabout 1-400, typically between about 5-100), that connect to patch bay135 and/or 137. Cabling 210 n for anesthesia cart 160 can also be routedthrough the ceiling (where n is typically between about 1-400, typicallybetween about 5-100). The cabling 200 n, 210 n extends through theceiling between the rooms 10 a, 10 b and can connect to the remotedevices 500 through a patch panel 250. In some embodiments foot pedalcabling 220 n can extend through a floor trough to the patchpanel/second room 10 b as well (where “n” is typically between about1-100 cables). For additional description of an exemplary cardiac suite,see, U.S. patent application Ser. No. 12/708,773, the contents of whichare hereby incorporated by reference as if recited in full herein. Thecables may also alternately be routed under, on or over the floor,suspended on walls, employ wireless connections and the like (andcombinations of same).

As is known to those of skill in the art, there are typically betweenabout 60-100 lesions generated during a single patient cardiac (AFIB) EPprocedure. Other cardiac procedures may only require about 1 ablation orless than 60. A typical patient interventional cardiac procedure lastsless than about 4 hours, e.g., about 1-2 hours. Each lesion site can beablated for between about 30 seconds to about 2 minutes. Lineartransmural lesions (such as “continuous” drag method lesions) may begenerated or “spot” lesions may be generated, depending on the selectedtreatment and/or condition being treated. The continuous lesion may beformed as a series of over lapping spot ablation lesions or as acontinuous “drag” lesion.

The system can include a monitoring circuit can automatically detectwhich devices are connected to the patient patch bay. One way this canbe achieved is by using ID resistors in the patch bay and/or interfaceas well as in various devices that connect thereto. The MRI scannercomputer or processor or the clinician workstation module or processorcan monitor resistors via connections CON1, CON2 and CON3. The devices80 (FIG. 1) can have built-in resistors that modify the resistance bylines that connect to CON1, CON2 and CON3. Variation in resistancevalues helps the monitor which device is connected. Once thatdetermination is made the scanner may automatically load specialacquisition parameters, display parameters and update the progress ofthe procedure to display on the display 20 such as at workstation 60(FIG. 3), for example.

Electrical isolation between the MR Scanner 10S and the device 80 can beprovided via low pass filters inside and outside the MRI suite. As isknown to those of skill in the art, components in the MRI Suite can beconnected to external components using a waveguide built into the RFshield that encloses the MRI suite. The ablation catheter 80 can beconnected to an appropriate energy source, such as, for example, aStockert 70 RF generator (Biosense Webster, Diamond Bar, Calif., USA)with MR compatible interface circuits configured for 3 T magnetic fields(where a 3 T system is used). The system can comprise an EP Suite with aSiemens Verio system (Siemens Healthcare, Erlangen, Germany) or othersuitable scanner as well as suitable external imaging coils, such asspine and/or body array coils as is known to those of skill in the art.

Embodiments of the present invention may be utilized in conjunction withnavigation and mapping software features. For example, current and/orfuture versions of devices and systems described herein may includefeatures with adaptive projection navigation and/or 3-D volumetricmapping technology, the latter may include aspects associated with U.S.patent application Ser. No. 10/076,882, which is incorporated herein byreference in its entirety.

Although described primarily herein with respect to Cardiac EPprocedures using ablation electrodes, other ablation techniques can beused, such as, for example, laser ablation, thermal (heated liquid)ablation and cryoablation. Similarly, the systems and componentsdescribed herein can be useful for other MRI guided cardiac surgicalintervention procedures, including, for example, delivering biologics orother drug therapies to target locations in cardiac tissue using MRI.

Some interventional tools may include an MRI receive antenna forimproved SNR of local tissue. In some embodiments, the antenna has afocal length or signal-receiving length of between about 1-5 cm, andtypically is configured to have a viewing length to receive MRI signalsfrom local tissue of between about 1-2.5 cm. The MRI antenna can beformed as comprising a coaxial and/or triaxial antenna. However, otherantenna configurations can be used, such as, for example, a whipantenna, a coil antenna, a loopless antenna, and/or a looped antenna.See, e.g., U.S. Pat. Nos. 5,699,801; 5,928,145; 6,263,229; 6,606,513;6,628,980; 6,284,971; 6,675,033; and 6,701,176, the contents of whichare hereby incorporated by reference as if recited in full herein. Seealso U.S. Patent Application Publication Nos. 2003/0050557;2004/0046557; and 2003/0028095, the contents of which are also herebyincorporated by reference as if recited in full herein. Image data canalso include image data obtained by a trans-esophageal antenna catheterduring the procedure. See, e.g., U.S. Pat. No. 6,408,202, the contentsof which are hereby incorporated by reference as if recited in fullherein.

As discussed above, embodiments of the present invention may take theform of an entirely software embodiment or an embodiment combiningsoftware and hardware aspects, all generally referred to herein as a“circuit” or “module.” Furthermore, the present invention may take theform of a computer program product on a computer-usable storage mediumhaving computer-usable program code embodied in the medium. Any suitablecomputer readable medium may be utilized including hard disks, CD-ROMs,optical storage devices, a transmission media such as those supportingthe Internet or an intranet, or magnetic storage devices. Some circuits,modules or routines may be written in assembly language or evenmicro-code to enhance performance and/or memory usage. It will befurther appreciated that the functionality of any or all of the programmodules may also be implemented using discrete hardware components, oneor more application specific integrated circuits (ASICs), or aprogrammed digital signal processor or microcontroller. Embodiments ofthe present invention are not limited to a particular programminglanguage.

Computer program code for carrying out operations of data processingsystems, method steps or actions, modules or circuits (or portionsthereof) discussed herein may be written in a high-level programminglanguage, such as Python, Java, AJAX (Asynchronous JavaScript), C,and/or C++, for development convenience. In addition, computer programcode for carrying out operations of exemplary embodiments may also bewritten in other programming languages, such as, but not limited to,interpreted languages. Some modules or routines may be written inassembly language or even micro-code to enhance performance and/ormemory usage. However, embodiments are not limited to a particularprogramming language. It will be further appreciated that thefunctionality of any or all of the program modules may also beimplemented using discrete hardware components, one or more applicationspecific integrated circuits (ASICs), or a programmed digital signalprocessor or microcontroller. The program code may execute entirely onone (e.g., a workstation computer or a Scanner's computer), partly onone computer, as a stand-alone software package, partly on theworkstation's computer or Scanner's computer and partly on anothercomputer, local and/or remote or entirely on the other local or remotecomputer. In the latter scenario, the other local or remote computer maybe connected to the user's computer through a local area network (LAN)or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider).

The present invention is described in part with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products according to embodiments of the invention. Itwill be understood that each block of the flowchart illustrations and/orblock diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing some or all of thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowcharts and block diagrams of certain of the figures hereinillustrate exemplary architecture, functionality, and operation ofpossible implementations of embodiments of the present invention. Inthis regard, each block in the flow charts or block diagrams representsa module, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that in some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the figures. For example, two blocks shown in successionmay in fact be executed substantially concurrently or the blocks maysometimes be executed in the reverse order or two or more blocks may becombined, depending upon the functionality involved.

The workstation 60 and/or interface 44, 84, or patch bay, may alsoinclude a decoupling/tuning circuit that allows the system to cooperatewith an MRI scanner 10S and filters and the like. See, e.g., U.S. Pat.Nos. 6,701,176; 6, 904,307 and U.S. Patent Application Publication No.2003/0050557, the contents of which are hereby incorporated by referenceas if recited in full herein. In some embodiments, the intrabody device80 is configured to allow for safe MRI operation so as to reduce thelikelihood of undesired deposition of current or voltage in tissue(inhibit or prevent undesired heating). The device 80 can include RFchokes such as a series of axially spaced apart Balun circuits or othersuitable circuit configurations. See, e.g., U.S. Pat. No. 6,284,971, thecontents of which are hereby incorporated by reference as if recited infull herein, for additional description of RF inhibiting coaxial cablethat can inhibit RF induced current. The conductors connectingelectrodes or other components on or in the catheter (or otherinterventional device) can also include a series of back and forthsegments (e.g., the lead can turn on itself in a lengthwise direction anumber of times along its length) and/or include high impedancecircuits. See, e.g., U.S. patent application Ser. Nos. 11/417,594;12/047,602; and 12/090,583, the contents of which are herebyincorporated by reference as if recited in full herein.

Although not shown, in some embodiments, the device can be configuredwith one or more lumens and exit ports and can be used and/or deliverdesired cellular, biological, and/or drug therapeutics to a target area.

FIG. 30 is a schematic illustration of a circuit or data processingsystem 190 that can be used with the system 10. The circuits and/or dataprocessing systems 190 may be incorporated in a digital signal processorin any suitable device or devices. As shown in FIG. 30, the processor310 communicates with and/or is integral with an MRI scanner 10S andwith memory 314 via an address/data bus 348. The processor 310 can beany commercially available or custom microprocessor. The memory 314 isrepresentative of the overall hierarchy of memory devices containing thesoftware and data used to implement the functionality of the dataprocessing system. The memory 314 can include, but is not limited to,the following types of devices: cache, ROM, PROM, EPROM, EEPROM, flashmemory, SRAM, and DRAM.

FIG. 30 illustrates that the memory 314 may include several categoriesof software and data used in the data processing system: the operatingsystem 349; the application programs 360; the input/output (I/O) devicedrivers 358; and data 355. The data 355 can also include device(ablation catheter) dimensions (e.g., distance of a tracking coil to thetip) and patient-specific image data 355. FIG. 30 also illustrates theapplication programs 354 can include a Tracking Coil LocationIdentification Calculation Module 350, a Visualization Rendering Module352, an Interactive Visualization (and UI) Module 353, a TissueCharacterization Map Module 356, and a Pre-Set Scan Plane to TargetAblation Site Module 354, a and a UI Interface Module 353.

As will be appreciated by those of skill in the art, the operatingsystems 349 may be any operating system suitable for use with a dataprocessing system, such as OS/2, AIX, or z/OS from InternationalBusiness Machines Corporation, Armonk, N.Y., Windows CE, Windows NT,Windows95, Windows98, Windows2000, WindowsXP, Windows Visa, Windows7,Windows CE or other Windows versions from Microsoft Corporation,Redmond, Wash., Palm OS, Symbian OS, Cisco IOS, VxWorks, Unix or Linux,Mac OS from Apple Computer, LabView, or proprietary operating systems.For example, VxWorks which can run on the Scanner's sequence generatorfor precise control of pulse sequence waveform timings.

The I/O device drivers 358 typically include software routines accessedthrough the operating system 349 by the application programs 360 tocommunicate with devices such as I/O data port(s), data storage 356 andcertain memory 314 components. The application programs 360 areillustrative of the programs that implement the various features of thedata processing system and can include at least one application, whichsupports operations according to embodiments of the present invention.Finally, the data 356 represents the static and dynamic data used by theapplication programs 360, the operating system 349, the I/O devicedrivers 358, and other software programs that may reside in the memory314.

While the present invention is illustrated, for example, with referenceto the Modules 350, 352, 353, 354, 356 being application programs inFIG. 30, as will be appreciated by those of skill in the art, otherconfigurations may also be utilized while still benefiting from theteachings of the present invention. For example, the Modules and/or mayalso be incorporated into the operating system 349, the I/O devicedrivers 358 or other such logical division of the data processingsystem. Thus, the present invention should not be construed as limitedto the configuration of FIG. 30 which is intended to encompass anyconfiguration capable of carrying out the operations described herein.Further, one or more of modules, i.e., Modules 350, 352, 353, 354, 356can communicate with or be incorporated totally or partially in othercomponents, such as separate or a single processor, an MRI scanner 10Sor workstation 60.

The I/O data port can be used to transfer information between the dataprocessing system, the workstation, the MRI scanner, and anothercomputer system or a network (e.g., the Internet) or to other devicescontrolled by the processor. These components may be conventionalcomponents such as those used in many conventional data processingsystems, which may be configured in accordance with the presentinvention to operate as described herein.

Non-Limiting Examples of Tissue Characterization Maps will be discussedbelow.

Thermal Tissue Characterization Map

The thermal tissue characterization map can be based on thermal statusat a given point in time or may be provided as a composite of heating ofdifferent tissue locations at different times (e.g., during and/or afterablation of different points at different times of the ablationprocedure). The thermal map can be registered to a location of theinternal ablation catheter (e.g., tip) at different times so that thelocation of the ablation catheter tip is correlated to the thermalactivity/status at that location at that time as that is the time framethat the image data for that region illustrating increased thermalactivity/heating is generated. That is, the image scan planes are takento show the tissue at the location of the ablation catheter tip. Theimage scan planes are typically projected forward a known distance fromthe tracking coil so that the lesion tissue in front of the ablation tipis imaged.

The MR thermal data can be obtained using temperature imaging techniques(MR thermometry) to show temperature or phase variance. Examples ofpulse sequences include, for example, SSFP and 2D GRE.

Vasculature Tissue Characterization Map

Segmented MRA (Magnetic Resonance Angiography) imaging volumes of apatient can be used to generate a vasculature tissue characteristic mapwhich may indicate areas of increased blood flow and/or larger andsmaller channels within the vasculature structure.

Fibrous Tissue Characterization Map

Contrast-based or non-contrast based MRI images of the patient canidentify fibrous tissue in target tissue (e.g., the heart).

Contrast-Based Tissue Characterization Maps

Tissue damage can be shown or detected using MR image data based oncontrast agents such as those agents that attach to or are primarilyretained in one of, but not both, healthy and unhealthy tissue, e.g.,the contrast agent is taken up by, attaches to, or resides or stays inone more than in the other so that MR image data will visually indentifythe differences (using pixel intensity). The contrast agent can be oneor more of any known or future developed biocompatible agent, currentlytypically gadolinium, but may also include an antibody or derivative orcomponent thereof that couples to an agent and selectively binds to anepitope present in one type of tissue but not the other (e.g., unhealthytissue) so that the epitope is present in substantially amounts in onetype but not the other. Alternatively, the epitope can be present inboth types of tissue but is not susceptible to bind to one type bysteric block effects.

A tissue characteristic map registered to the imaging space can allow aclinician to assess both scar formation (isolation of the PV) and thevolume of enhancement on a LA myocardial volume may indicate a pooroutcome prediction and a clinician may decide to continue ablating oralter the ablation location or protocol (e.g., drive a clinicaldecision).

Examples of pulse sequences that can be used for delayedhyper-enhancement MRI include, for example, gradient echo, SSFP (steadystate free precession) such as TrueFISP on Siemens MRI Scanners, FIESTAon GE MRI Scanners, and b-FFE on Philips MRI Scanners.

Edema Tissue Characterization Maps

After (and/or during) ablation, tissue will typically have edema. Thiscan be detected in MRI using, for example, pulse sequences such asT2-weighted Turbo-Spin-Echo, HASTE (a Siemens term), SSFP, orT2-weighted gradient recalled echo (GRE).

Some tissue characterization maps may show edema and thermal mapsoverlaid or otherwise combined as a composite map that can be used toevaluate a procedure. For example, to visually assess whether there iscomplete or incomplete scar formation to isolate pulmonary veins. It isbelieved that complete scar formation to isolate PV is associated with abetter prognosis for AFIB.

Heart Wall Motion Tissue Characterization Maps

MRI can be used to assess heart wall motion. Abnormal motion can bevisually indicated on the tissue characterization map. Examples of pulsesequences that may be used to determine heart wall motion include, forexample, DENSE, HARP and MR tagging.

Thus, it will be appreciated that embodiments of the present inventionare directed to systems, including hardware and/or software and relatedmethodology to substantially continuously collect and construct,throughout an MRI-guided cardiac procedure, e.g., an MRI-guidedprocedure, a patient-specific anatomical tissue characterization map orassociated data that can be shown on a map of a target anatomicalstructure/region (e.g., a chamber of the heart such as the atrium).Embodiments of the system can generate and show in pre-set views and innear-real time during the procedure tissue while it is being treated,e.g., ablated.

While embodiments have been primarily discussed with respect to anMRI-guided cardiac system, the system can be used for other anatomicalregions and deliver or apply other therapies as well as for diagnosticprocedures. For example, the esophagus and anatomy near the esophagus,e.g., the aorta, coronary arteries, mediastinum, the hepaticobiliarysystem or the pancreas in order to yield anatomic information about thestructures in those areas, “pancreaticohepaticobiliary” structures(collectively the structures of the liver, gallbladder, bile ducts andpancreas), the tracheobronchopulmonary structure (structures includingthe lungs and the tracheobronchial tree), the nasopharynx system (e.g.,a device introduced transnasally may be adapted for evaluating thearterial circle of Willis and related vascular structures forabnormalities, for example congenital or other aneurysms), the proximalaerodigestive system or the thyroid, the ear canal or the Eustachiantube, permitting anatomic assessment of abnormalities of the middle orinner ear, and further permitting evaluation of adjacent intracranialstructures and lesions.

The systems and methods of the present invention may be particularlyuseful in those lesions whose extent is not readily diagnosed, such asbasal cell carcinomas. These lesions may follow nerves into the orbit orinto the intracranial area, extensions not evident with traditionalimaging modalities to the surgeon undertaking the resection to providereal time information to the resecting surgeon or the surgeon performinga biopsy as to the likely areas of lymph node invasion.

It is also contemplated that the systems can be used in the “head andneck” which refers collectively to those structures of the ear, nose andthroat and proximal aerodigestive system as described above,traditionally falling within the province of otorhinolaryngology. Theterm “head and neck,” as used herein, will further include thosestructures of the neck such as the thyroid, the parathyroid, the parotidand the cervical lymph nodes, and will include also the extracranialportions of the cranial nerves, including but not limited to the facialnerve, this latter nerve being included from its entry into the internalauditory meatus outward. The term “head and neck, as used herein, willalso include those structures of the orbit or of the globe, includingthe oculomotor muscles and nerves, lacrimal glands and adnexalstructures. As used herein, the term “head and neck” will furtherinclude those intracranial structures in proximity to the aforesaid headand neck structures. These intracranial structures may include, asexamples, the pituitary gland, the pineal gland, the nuclei of variouscranial nerves, the intracranial extensions of the cranial nerves, thecerebellopontine angle, the arterial circle of Willis and associatedvascular structures, the dura, and the meninges.

In yet other embodiments, the systems can be used in the genourinarysystem, such as the urethra, prostate, bladder, cervix, uterus, andanatomies in proximity thereto. As used herein, the term “genitourinary”shall include those structures of the urinary tract, the male genitalsystem and the female genital system. The urinary tract structuresinclude the urethra, the bladder, the ureters, the kidney and relatedneural, vascular, lymphatic and adnexal structures. The male genitaltract includes the prostate, the seminal vesicles, the testicles, theepididymis and related neural, vascular, lymphatic, ductal and adnexalstructures. The female genital tract includes the vagina, the cervix,the non-gravid and gravid uterus, the fallopian tubes, the ovaries, theova, the fertilized egg, the embryo and the fetus. The term“genitourinary” further refers to those pelvic structures that surroundor support the above-mentioned structures, such as the paraurethraltissues, the urogenital diaphragm or the musculature of the pelvicfloor. The devices can be configured for transurethral placement forevaluation and treatment of female urinary incontinence or bleeding andmay use high resolution images of the local tissue, e.g., differentlayers of the paraurethral tissues. It is understood, for example, thata clearly identified disruption in the muscle layers surrounding theurethra may be repaired surgically, but also must be guided by detailedanatomic information about the site of the abnormality. The devices mayalso be configured for placement in the genitourinary system such asinto the ureter or renal pelvis, urinary tract, or transvaginal use inanalysis of the vagina and anatomies in proximity thereto. For example,transvaginal or transcervical endouterine placement may be useful in thediagnosis of neoplasia, in the diagnosis and treatment of endometriosisand in the evaluation of infertility or diagnosis, treatment of pelvicdisorders resulting in pelvic pain syndromes, evaluation/treatment ofcervical and uterine malignancies and to determine their stages,obstetric use such as permitting anatomic evaluation of mother andfetus.

In another embodiment, the systems can be used for evaluating and/ortreating the rectum or colon, typically by the transrectal route thatcan be inserted through the anus to a level within the rectum, sigmoidor descending colon where the designated anatomy can be visualized. Forexample, this approach may be used to delineate the anatomy of theprostate gland, and may further guide the biopsy or the extirpation oflesions undertaken transrectally or transurethrally.

In other embodiments, the systems and methods of the present inventionmay be used for the evaluation, diagnosis or treatment of a structure inthe gastrointestinal system, or for the evaluation, diagnosis ortreatment of a region of the gastrointestinal anatomy. As used herein,the term “gastrointestinal” shall include structures of the digestivesystem including the esophagus, the stomach, the duodenum, jejunum andileum (small intestine), the appendix and the colon. The term“gastrointestinal anatomy” shall refer to the structures of thegastrointestinal system as well as the surrounding supporting structuressuch as the mesentery and the enclosing structures such as theperitoneum, the diaphragm and the retroperitoneum. Disorders of thegastrointestinal system are well-known in the medical arts, as aredisorders of the gastrointestinal anatomy. In an exemplary embodiment,the intrabody device may be passed into the stomach.

In other embodiments, the systems and methods of the present inventionmay be used for the evaluation, diagnosis and treatment of the vascularsystem. The vascular system is understood to include the blood vesselsof the body, both arterial and venous. The vascular system includes bothnormal and abnormal blood vessels, named and unnamed vessels, andneovascularization. Access to the vascular system takes place usingtechniques familiar to practitioners of ordinary skill in the art. Thepresent invention may be used in blood vessels of all size and theintrabody devices may be dimensionally adapted to enter smaller calibervessels, such as those comprising the distal coronary circulation, theintracranial circulation, the circulation of the distal extremities orthe distal circulation of the abdominal viscera. According to thesesystems and methods, furthermore, positioning a device within thevascular system may be useful for evaluating, diagnosing and treatingconditions in structures adjacent to or in proximity to the particularvessel within which the device is situated. Such structures are termed“perivascular structures.” As an example, a device placed within acoronary artery may provide information about the vessel itself andabout the myocardium that is perfused by the vessel or that is adjacentto the vessel. A device thus positioned may be able to guide therapeuticinterventions directed to the myocardial tissue, and may also be able toguide endovascular or extravascular manipulations directed to the vesselitself. It will be readily appreciated by those of ordinary skill in theart that a number of other applications exist or may be discovered withno more than routine experimentation using the systems and methods ofthe present invention within the vascular system.

It is understood that access to anatomic structures using the systems,devices modified to fit the intended purpose and anatomy, and methods ofthe present invention may be provided via naturally occurring anatomicorifices or lumens, as indicated in the examples above. It is furtherunderstood, however, that access to anatomic structures using thesesystems and methods may be additionally provided using temporary orpermanent orifices that have been created medically.

Further, the methods and systems may cooperate with robotic drivensystems rather than manual systems.

Ablation Catheter

Referring to FIGS. 31-46, a flexible (steerable) ablation catheter 80for use in MRI-guided ablation procedures, according to some embodimentsof the present invention, is illustrated. The ablation catheter 80includes an elongated flexible housing or shaft 402 having at least onelumen 404 (FIG. 34) therethrough and includes opposite distal andproximal end portions 406, 408, respectively. The distal end portion 406includes an ablation tip 410 having an ablation electrode 410 e (FIG.33) for ablating target tissue. A pair of RF tracking coils individuallyidentified as 412, 414, and which are equivalent to coils 82 c of FIGS.2-3, are positioned upstream from the ablation tip 410, as illustrated.The ablation tip 410 can include a second electrode for sensing localelectrical signals or properties, or the ablation electrode 410 e can bebipolar and both ablate and sense.

The proximal end portion 408 of the catheter 80 is operably secured to ahandle 440. The catheter shaft 402 is formed from flexible,bio-compatible and MRI-compatible material, such as, for example,polyester or other polymeric materials. However, various other types ofmaterials may be utilized to form the catheter shaft 402, andembodiments of the present invention are not limited to the use of anyparticular material. In some embodiments, the shaft proximal end portion408 is formed from material that is stiffer than the distal end portion406. The proximal end may be stiffer than a medial portion between thedistal and proximal end portions 406, 408.

The catheter 80 can be configured to reduce the likelihood of undesiredheating caused by deposition of current or voltage in tissue. Thecatheter 80 can include RF chokes such as a series of axially spacedapart Balun circuits or other suitable circuit configurations. See,e.g., U.S. Pat. No. 6,284,971 for additional description of RFinhibiting coaxial cable that can inhibit RF induced current.

FIGS. 32A and 32B illustrate the distal end portion 406 of the ablationcatheter 80 of FIG. 31 in a substantially elongated configuration (FIG.32A) and in an articulated and/or curvilinear configuration (FIG. 32B),respectively. The ability to articulate and/or bend and/or deform thedistal end portion 406 facilitates positioning the ablation tip 410 atdesired locations (e.g., within a heart) during an ablation procedure.The term “articulation”, as used herein, is intended to include all waysthat the ablation tip portion 410 can be moved or modified or shaped(e.g., curvilinear movement, deforming movement, etc.).

In the illustrated embodiment, articulation of the distal end portion406 is achieved by movement of a pull wire 436 (FIG. 37) disposed withinthe catheter shaft 402. Movement of the pull wire 436 is accomplishedvia the handle 440 at the catheter proximal end portion 408, as will bedescribed below. The handle 440 serves as an actuator in conjunctionwith the pull wire 436 to articulate the distal end portion 406. Varioustypes of actuators may be utilized (e.g., levers, pistons, thumbsliders, knobs, etc.). Embodiments of the present invention are notlimited to the illustrated handle and pull wire actuator.

FIG. 33 is an enlarged partial perspective view of the distal endportion 406 of the ablation catheter 80 of FIG. 31. The distal endportion 406 has an ablation tip 410 and typically at least two RFtracking coils 412, 414. The RF tracking coils 412, 414 are positionedupstream and adjacent the ablation tip 410 in spaced-apart relationship.The RF tracking coils 412, 414 are each electrically connected to arespective channel of an MRI scanner for tracking the location of thecatheter 80 in 3-D space, via respective cables (e.g., coaxial cables)416, 418 (FIG. 34) extending longitudinally through the catheter shaftlumen 404 and terminating at an electrical connector interface 450 inthe handle 440 (FIG. 43). In the illustrated embodiment of FIG. 33, theRF tracking coils 412, 414 are supported within respective coil holders415 that are secured to the catheter shaft 402, as illustrated. The RFtracking coils 412, 414 can be closely spaced and, in some embodiments,may be within about 12 mm from the ablation tip 410. In someembodiments, the RF tracking coils 412, 414 may each have about 2-16turns and may have a length L in the longitudinal direction of thecatheter shaft 402 of between about 0.25 mm and about 4 mm. Embodimentsof the present invention are not limited to the two illustrated RFtracking coils 412, 414. RF tracking coils with other turns andlongitudinal lengths may be used. In addition, one or more than two RFtracking coils (e.g., 1, 3, 4, etc.) may be located at distal endportion 406, according to other embodiments of the present invention.

As shown, for example in FIG. 34, each coil holder 415 has a respectiverecessed portion 415 a within which a respective RF tracking coil 412,414 is disposed. Each recessed portion 415 a has a radial depth suchthat each respective coil 412, 414 is recessed slightly with respect tothe outer surface 402 a of the catheter shaft 402. In other embodiments,each recessed portion 415 a may have a radial depth such that eachrespective coil is substantially flush with the outer surface 402 a ofthe catheter shaft 402. In other embodiments, the RF tracking coils 412,414 may be embedded within the shaft 402. Tracking coil 412 may bereferred to as the tip distal coil and tracking coil 414 may be referredto as the tip proximal coil. In some embodiments, the tracking coils412, 414 may be covered with a layer of material (not shown). Forexample, a layer of polymeric material, epoxy, etc. may be utilized.Each coil 412, 414 may be recessed within each respective coil holder415 such that the layer of material overlying the coils 412, 414 issubstantially flush with the outer surface 402 a of the catheter 80.

In the illustrated embodiment, the ablation tip 410 includes anelectrode 410 e that is connected to an RF wire 420 that extendslongitudinally within the lumen 404 to the electrical connectorinterface 450 (FIG. 44) within the handle 440 and that connects theablation electrode 410 e to an RF generator. The RF ablation electrode410 e is formed from a conductive material capable of receiving RFenergy and ablating tissue. Exemplary materials include copper, as wellas bio-compatible materials such as platinum, etc. In other embodiments,the ablation tip 410 may include a cryogenic ablation electrode/deviceconfigured to cryogenically ablate tissue. For example, the ablationcatheter 80 can also or alternatively be configured to apply otherablation energies including cryogenic (e.g., cryoablation), laser,microwave, and even chemical ablation. In some embodiments, the ablationcan be carried out using ultrasound energy. In particular embodiments,the ablation may be carried out using HIFU (High Intensity FocusedUltrasound). When MRI is used this is sometimes called MagneticResonance-guided Focused Ultrasound, often shortened to MRgFUS. Thistype of energy using a catheter to direct the energy to the targetcardiac tissue can heat the tissue to cause necrosis.

The conductors 81 and/or RF wire 420 can include a series of back andforth segments (e.g., it can turn on itself in a lengthwise direction anumber of times along its length), include stacked windings and/orinclude high impedance circuits. See, e.g., U.S. patent application Ser.Nos. 11/417,594; 12/047,832; and 12/090,583, the contents of which arehereby incorporated by reference as if recited in full herein. Theconductors (e.g., coaxial cables) 81 and/or RF wire 420 can be co-woundand/or configured as back and forth stacked segments for a portion orall of their length.

Referring to FIG. 35, the catheter distal end portion 406 of theablation catheter 80 can include a second pair of RF tracking coils 422,424 in spaced apart relationship, as illustrated. The illustrated RFtracking coils 422, 424 are disposed within recessed portions 402 b ofthe catheter shaft 402. Each recessed portion 402 b has a radial depthsuch that each respective RF tracking coil 422, 424 is recessed slightlywith respect to the outer surface 402 a of the catheter shaft 402. Insome embodiments, however, each recessed portion 402 b may have a radialdepth such that each respective RF tracking coil 422, 424 issubstantially flush with the outer surface 402 a of the catheter shaft402. In other embodiments, the RF tracking coils 422, 424 may beembedded within the shaft 402. Each illustrated RF tracking coil 422,424 is connected to a respective coaxial cable 426, 428 (FIG. 38) thatextends longitudinally within the lumen 404 to the electrical connectorinterface 450 (FIG. 43) within the handle 440.

In some embodiments, the tracking coils 422, 424 may be covered with alayer of material (not shown). For example, a sleeve or layer ofpolymeric material, epoxy, etc. may be utilized. Each coil 422, 424 maybe recessed within the catheter shaft 402 such that the layer ofmaterial overlying the coils 422, 424 is substantially flush with theouter surface 402 a of the catheter 80. In some embodiments, asillustrated in FIG. 53, all four RF tracking coils 412, 414, 422, 424may be covered with a sleeve or layer of material 480, such as a sleeveof heat shrink material having a thickness of about 0.003 inches.

Referring to FIG. 38, in some embodiments of the present invention thecatheter 80 includes a thermocouple 430 that has a lead that extendslongitudinally within the shaft lumen 404 from the ablation tip 410 tothe electrical connector interface 450. The thermocouple 430 isconfigured to measure temperature of at and/or adjacent to the ablationtip 410. The thermocouple 430 can be configured to allow temperature tobe monitored during ablation and/or at other times.

In some embodiments, the ablation tip 410 is provided with one or moreexit ports 432 (FIG. 33) in communication with a fluid channel throughwhich a fluid/solution, such as saline, can flow before, during, and/orafter the ablation of tissue. Fluid/solution is provided to the one ormore exit ports 432 via an irrigation lumen 434 that extendslongitudinally through the catheter shaft lumen 404 from the exitport(s) 432 to the handle 440. The irrigation lumen 434 is in fluidcommunication with a fluid/solution source at the proximal end portion408 of the catheter shaft, typically at the handle 440. Thefluid/solution can provide coolant and/or improve tissue coupling withthe ablation tip 410.

In some embodiments, as noted above, a pull wire 436 (FIG. 38) extendslongitudinally within the catheter shaft lumen 404 from the distal endportion 406 to the handle 440 at the catheter proximal end portion 408.The pull wire 436 can extend longitudinally within a sleeve 438 that isattached to the internal wall 404 a of the lumen 404. The pull wire 436is attached to the sleeve 438 near the distal end portion 406 of thecatheter 80 and otherwise is slidably disposed within the sleeve.Pulling the pull wire 436 in a direction towards the handle 440 causesthe distal end portion 406 of the catheter to articulate in onedirection. Pushing the pull wire 436 in the opposite direction away fromthe handle 440 causes the distal end portion 406 to articulate inanother different direction. In some embodiments, the distal end portion406 may include a biasing member, such as a spring, for returning thearticulated distal end portion 406 to a non-articulated position.

The pull wire 436 may comprise various non-metallic materials including,but not limited to, non-metallic wires, cables, braided wires, etc. Insome embodiments a mono-filament wire may be utilized. In otherembodiments, a multi-filament wire and/or a braided wire may beutilized. Exemplary filament materials may include, but are not limitedto, Kevlar® filaments and Aramid® filaments.

FIGS. 37 and 39 are cross sectional views of the distal end portion 406of the illustrated catheter 80. FIG. 37 is a cross sectional view takenalong lines 37-37 in FIG. 35 and illustrates the location andconfiguration of the coaxial cables 416, 418, 426 and 428 which areconnected to the RF tracking coils 412, 414, 422 and 424, respectively.FIG. 37 also illustrates the location and configuration of an RF wire420 that is connected to the ablation tip 410 and that provides RFenergy to the ablation electrode 410 e. FIG. 37 also illustrates thelocation of the thermocouple 430, and the location of an irrigationlumen 434. FIG. 39 is a cross sectional view taken along lines 30-30 inFIG. 38 and illustrates the location and configuration of the coaxialcables 416, 418 which are connected to the RF tracking coils 412, 414.FIG. 39 also illustrates the location and configuration of the RF wire420 connected to the ablation electrode 410 e, the location ofthermocouple 430, and the location of irrigation lumen 434.

FIG. 40 is a cross-sectional view of the illustrated catheter 80 at thesame location as the cross-sectional view of FIG. 39 and thatillustrates an exemplary diameter or free space available inside the tipassembly 401, according to some embodiments of the present invention.FIG. 40 also illustrates the respective diameters of the thermocouple430, coaxial cables 416, 418, pull wire 436, sleeve 438, and RF wire420. FIG. 41 is a cross-sectional view of the illustrated ablationcatheter 80 at the same location as the cross-sectional view of FIG. 37and that illustrates an exemplary diameter or free space availableinside the catheter shaft lumen 404, according to some embodiments ofthe present invention. FIG. 41 also illustrates the respective diametersof the thermocouple 430, coaxial cables 416, 418, pull wire 436, sleeve438, and the RF wire 420. FIG. 42 is a cross-sectional view of theillustrated catheter 80 that illustrates an exemplary number of wiresthat can be placed inside the catheter shaft lumen 404, according tosome embodiments of the present invention.

FIG. 43 is a perspective view of the handle 440, which is connected tothe proximal end portion 408 of the catheter shaft 402, according tosome embodiments of the present invention. The handle 440 has a mainbody portion 441 with opposite distal and proximal end portions 442,444. In FIG. 43, a cover 443 (FIG. 44) is removed from the handle mainbody portion 441 to illustrate the termination of the various leadsextending into the handle 440 from the shaft lumen 404 at an electricalconnector interface 450 (shown as PCB). Electrical connector interface450 is electrically connected to an adapter 452 at the proximal end 444of the handle 440. Adapter 452 is configured to receive one or morecables that connect the ablation catheter 80 to an MRI scanner 10S andthat facilitate operation of the RF tracking coils 412, 414, 422, 424.Adapter 452 also is configured to connect the ablation tip 410 to anablation source. In the illustrated embodiment, electrical connectorinterface 450 can also include the decoupling circuit 460, describedbelow.

In the illustrated embodiment, the distal end portion 442 of the handle440 includes a piston 446 that it movably secured to the handle mainbody portion 441 and that is movable between extended and retractedpositions relative the handle main body portion 441. In FIG. 43, thepiston 446 is in a retracted position. The piston 446 is connected tothe pull wire 436 such that movement of the piston 446 between extendedand retracted positions causes the pull wire 436 to correspondinglyextend and retract and, thereby, causing articulation of the distal endportion 401 of the catheter 80.

FIG. 44 is an exploded perspective view of the handle 440 of FIG. 43,according to some embodiments of the present invention. The electricalconnector interface 450 is illustrated within the main body portion 441and the adapter 452 that is electrically connected to the electricalconnector interface 450 is illustrated at the handle proximal endportion 444. FIG. 45 is a perspective view of the handle 440 of FIG. 44with the piston 446 in a retracted position and the cover 443 secured tothe main body portion 441 via fasteners 447.

Referring to FIG. 46, another RF tracking coil tuning circuit 460 thatmay be utilized with individual MRI channels and respective RF trackingcoils 412, 414, 422, 424, according to some embodiments of the presentinvention, is illustrated. In the illustrated embodiment, eachrespective coaxial cable 416, 418, 426, 428 is about a 50 ohm impedancemicro-coaxial cable with a length from the diode of about ¾λ at about123.3 MHz (e.g., about 45 inches). However, other cables and/or cablelengths may be utilized in accordance with embodiments of the presentinvention, such as ¼λ lengths, or other odd harmonic/multiples of aquarter wavelength at an MRI Scanner operational frequency, etc. Foreach coaxial cable 416, 418, 426, 428, a respective RF tracking coil412, 414, 422, 424 is connected at one end and the tracking coil circuit460 is connected to the other end, as illustrated.

Each tracking coil circuit (460, FIG. 46; 83, FIG. 4) can include a PINdiode (462, FIG. 46; UI, FIG. 4) and DC blocking capacitor 464 (FIG. 46)and is typically located within the handle 440, although in otherembodiments, the tracking coil circuits 460 can be located within thecatheter shaft lumen 404 closer to a medial or distal end portion (notshown). Each tracking coil circuit 460 is electrically connected to anMRI scanner, and can reduce signal noise within a respective channelcaused by undesired coupling during scanner operation. In someembodiments, the tracking coil circuit 460 can produce 100 ohmsimpedance across an RF tracking coil when the PIN diode 462 is shorted,for example, by an MRI scanner during scanner operations, as illustratedin FIG. 49.

In some embodiments of the present invention, RF tracking coils 412,414, 422, 424 may be between about 2-16 turn solenoid coils. However,other coil configurations may be utilized in accordance with embodimentsof the present invention. Each of the RF tracking coils 412, 414, 422,424 can have the same number of turns or a different number of turns, ordifferent ones of the RF tracking coils 412, 414, 422, 424 can havedifferent numbers of turns. It is believed that an RF tracking coil withbetween about 2-4 turns at 3.0 T provides a suitable signal for trackingpurposes.

FIG. 47A illustrates an ablation catheter 80 in a 3.0 Tesla (T) MRIenvironment without the use of the RF tracking coil circuit 460 for eachRF tracking coil (412, 414, 422, 424). The tracking coil at the tipportion (i.e., coil 412) is a 10 turn solenoid coil. Undesired couplingproduced in the MRI environment by the presence of the variouselectronic components and wires within the catheter 80 is clearlyillustrated, particularly in the vicinity of RF tracking coil 424. FIG.47B illustrates an MRI signal strength graph 470 of the MRI image ofFIG. 47A in the Z direction. The undesired coupling is clearlyillustrated in the graph region 472. FIG. 47C illustrates MRI signalstrength of the MRI image of FIG. 47A in the X direction.

FIG. 48A illustrates an ablation catheter 80 in a 3.0 T MRI environmentand where the RF tracking coil tuning circuit 460 of FIG. 46 is utilizedwith each RF tracking coil (412, 414, 422, 424) to control and reduceundesired coupling. The tracking coil at the tip portion is a 16 turnsolenoid coil. FIG. 48B illustrates MRI signal strength graph 470 of theMRI image of FIG. 48A in the Z direction. The absence of undesiredcoupling is clearly illustrated, both in the MRI image of FIG. 39A andin region 472 of the graph 470 of FIG. 48B. FIG. 48C illustrates MRIsignal strength of the MRI image of FIG. 48A in the X direction.

Mapping Catheter

Referring to FIG. 50, a flexible (steerable) mapping catheter 80 for usein MRI-guided procedures, according to some embodiments of the presentinvention, is illustrated. The mapping catheter 80 includes an elongatedflexible housing or shaft 602 with opposite distal and proximal endportions, only the distal end portion 606 is illustrated. The distal endportion 606 includes a plurality of electrodes 608 for sensing localelectrical signals or properties arranged in spaced-apart relationship,as illustrated. First and second electrodes 608 a, 608 b are positionedadjacent the tip 610 of the catheter 80. The remaining electrodes (608c-608 d, 608 e-608 f, 608 g-608 h, 608 i-608 j) are positioned upstreamfrom the first two electrodes 608 a-608 b, as illustrated

The proximal end portion of the catheter 80 is operably secured to ahandle, as is well known. The catheter shaft 602 is formed fromflexible, bio-compatible and MRI-compatible material, such as polyesteror other polymeric materials. However, various other types of materialsmay be utilized to form the catheter shaft 602, and embodiments of thepresent invention are not limited to the use of any particular material.In some embodiments, the shaft distal end portion 606 is formed frommaterial that is stiffer than the proximal end portion and a medialportion between the distal and proximal end portions.

The catheter 80 can be configured to reduce the likelihood of undesireddeposition of current or voltage in tissue. The catheter 80 can includeRF chokes such as a series of axially spaced apart Balun circuits orother suitable circuit configurations. See, e.g., U.S. Pat. No.6,284,971 for additional description of RF inhibiting coaxial cable thatcan inhibit RF induced current.

The mapping catheter 80 also includes a plurality of tracking coils 612,614, 616 (equivalent to coils 80 c, FIGS. 2-3) in spaced-apartrelationship, as illustrated. Tracking coil 612 is positioned betweenthe first pair of electrodes 608 a, 608 b, as illustrated. The catheter80 can comprise coaxial cables 81 that connect the tracking coils 612,614, 616 to an external device for tracking the location of the catheter80 in 3-D space. The conductors 81 can include a series of back andforth segments (e.g., it can turn on itself in a lengthwise direction anumber of times along its length), include stacked windings and/orinclude high impedance circuits. See, e.g., U.S. patent application Ser.Nos. 11/417,594; 12/047,832; and 12/090,583, the contents of which arehereby incorporated by reference as if recited in full herein. Theconductors (e.g., coaxial cables) 81 can be co-wound in one direction orback and forth in stacked segments for a portion or all of their length.

Articulation of the distal end portion 606 may be achieved by movementof a pull wire (not shown), as described above with respect to theablation catheter 80, or by another actuator in communication with thedistal end portion 606, as would be understood by one skilled in theart.

The electrodes 608 can be closely spaced and, in some embodiment, may bearranged in pairs that are spaced-apart by about 2.5 mm. In someembodiments, the RF tracking coils 612, 614, 616 may each have about2-16 turns and may have a length in the longitudinal direction of thecatheter shaft 602 of between about 0.25 mm and about 4 mm. Embodimentsof the present invention are not limited to the three illustrated RFtracking coils 612, 614, 616. RF tracking coils with other turns andlongitudinal lengths may be used. In addition, one or more than three RFtracking coils (e.g., 1, 4, 5, etc.) may be utilized, according to otherembodiments of the present invention.

Referring now to FIGS. 51A-51B, a flexible (steerable) ablation catheter80 for use in MRI-guided procedures, according to other embodiments ofthe present invention, is illustrated. The illustrated ablation catheter80 includes an elongated flexible housing or shaft 702 with oppositedistal and proximal end portions, only the distal end portion 706 isillustrated. The proximal end portion of the catheter 80 is operablysecured to a handle, as is well known. The catheter shaft 702 is formedfrom flexible, bio-compatible and MRI-compatible material, such aspolyester or other polymeric materials. However, various other types ofmaterials may be utilized to form the catheter shaft 702, andembodiments of the present invention are not limited to the use of anyparticular material. In some embodiments, the shaft distal end portion706 is formed from material that is stiffer than the proximal endportion and a medial portion between the distal and proximal endportions.

The catheter 80 can be configured to reduce the likelihood of undesireddeposition of current or voltage in tissue. The catheter 80 can includeRF chokes such as a series of axially spaced apart Balun circuits orother suitable circuit configurations. See, e.g., U.S. Pat. No.6,284,971, the contents of which are hereby incorporated by reference asif recited in full herein, for additional description of RF inhibitingcoaxial cable that can inhibit RF induced current.

The distal end portion 706 includes a plurality of electrodes 708 a-708d for sensing local electrical signals or properties arranged inspaced-apart relationship, as illustrated. The first electrode 708 a islocated adjacent to the ablation tip 710. The second electrode 708 b islocated approximately 5.8 mm from the ablation tip 710. The third andfourth electrodes 708 c, 708 d are located approximately 10.1 mm and 13mm, respectively, from the ablation tip 710.

The illustrated ablation catheter 80 also includes a plurality of RFtracking coils 712, 714, 716, 718 (equivalent to coils 80 c, FIGS. 2-3)in spaced-apart relationship. Tracking coil 712 is positioned betweenthe first and second electrodes 608 a, 608 b, and tracking coil 714 ispositioned between the third and fourth electrodes 608 c, 608 d, asillustrated. The catheter 80 can comprise coaxial cables 81 that connectthe tracking coils 712, 714, 716, 718 to an external device for trackingthe location of the catheter 80 in 3-D space. The conductors 81 caninclude a series of back and forth segments (e.g., it can turn on itselfin a lengthwise direction a number of times along its length), includestacked windings and/or include high impedance circuits. See, e.g., U.S.patent application Ser. Nos. 11/417,594; 12/047,832; and 12/090,583. Theconductors (e.g., coaxial cables) 81 can be co-wound in one direction orback and forth in stacked segments for a portion or all of their length.

Articulation of the distal end portion 706 may be achieved by movementof a pull wire (not shown), as described above, or by another actuatorin communication with the distal end portion 706, as would be understoodby one skilled in the art.

Referring now to FIGS. 52A-52C, a flexible (steerable) mapping catheter80 for use in MRI-guided procedures, according to other embodiments ofthe present invention, is illustrated. The illustrated catheter 80 is a“loop” catheter and includes an elongated flexible housing or shaft 802with opposite distal and proximal end portions, only the distal endportion 806 is illustrated. The proximal end portion of the catheter 80is operably secured to a handle, as is well known. The catheter shaft802 is formed from flexible, bio-compatible and MRI-compatible material,such as polyester or other polymeric materials. However, various othertypes of materials may be utilized to form the catheter shaft 802, andembodiments of the present invention are not limited to the use of anyparticular material. In some embodiments, the shaft distal end portion806 is formed from material that is stiffer than the proximal endportion and a medial portion between the distal and proximal endportions.

The catheter 80 can be configured to reduce the likelihood of undesireddeposition of current or voltage in tissue. The catheter 80 can includeRF chokes such as a series of axially spaced apart Balun circuits orother suitable circuit configurations. See, e.g., U.S. Pat. No.6,284,971, for additional description of RF inhibiting coaxial cablethat can inhibit RF induced current.

The distal end portion 806 is articulable to a “loop” shape, asillustrated and includes a plurality of RF tracking coils 812, 814, 816,818, 820 (equivalent to coils 80 c, FIGS. 2-3) in spaced-apartrelationship. The catheter 80 can comprise coaxial cables 81 thatconnect the tracking coils 812, 814, 816, 818, 820 to an external devicefor tracking the location of the catheter 80 in 3-D space. Theconductors 81 can include a series of back and forth segments (e.g., itcan turn on itself in a lengthwise direction a number of times along itslength), include stacked windings and/or include high impedancecircuits. See, e.g., U.S. patent application Ser. Nos. 11/417,594;12/047,832; and 12/090,583. The conductors (e.g., coaxial cables) 81 canbe co-wound in one direction or back and forth in stacked segments for aportion or all of their length.

Articulation of the distal end portion 806 may be achieved by movementof a pull wire (not shown), as described above, or by another actuatorin communication with the distal end portion 806, as would be understoodby one skilled in the art.

FIGS. 54A-54C are plots of signal to noise ratio to distance for X axis,Y axis, and Z axis projections, respectively, for a four tracking coilcatheter, according to some embodiments of the present invention, andwherein each coil has two turns. FIGS. 55A-55C are plots of signal tonoise ratio to distance for X axis, Y axis, and Z axis projections,respectively, for a four tracking coil catheter, according to someembodiments of the present invention, and wherein each coil has fourturns. FIG. 56 is a table comparing signal to noise ration for thecatheters of FIGS. 54A-54C and 55A-55C. The plots of FIGS. 54A-54C and55A-55C illustrate the viability of miniature RF tracking coils havingonly 2 turns and 4 turns, respectively. These plots show thesignificance of how effective the circuits (83, FIG. 4; 460, FIG. 46)are.

Referring now to FIGS. 57A-57C, the shaft 402 of the ablation catheter80 of FIGS. 31-46 may include a plurality of RF shields 900 coaxiallydisposed within the wall W of the shaft 402 in end-to-end spaced-apartrelationship. The RF shields 900 may be utilized with any of thecatheters described herein, including the catheters of FIGS. 50,51A-51B, 52A-52C. The RF shields 900 are configured to impede RFcoupling along the shaft 402 when exposed to an MRI environment.Although a pair of RF shields 900 are illustrated in FIG. 57A, it isunderstood that many additional RF shields 900 may be coaxially disposedwithin the elongated sheath wall W in end-to-end spaced-apartrelationship. Only two RF shields 900 are shown for ease ofillustration.

As more clearly shown in FIGS. 57B-57C, each RF shield 900 includes anelongated inner tubular conductor 902 having opposite end portions 902a, 902 b, an elongated dielectric layer 904 that coaxially surrounds theinner conductor 902, and an elongated outer tubular conductor 906 thatcoaxially surrounds the dielectric layer 904 and has opposite endportions 906 a, 906 b. The inner and outer tubular conductors 902, 906are electrically connected to each other at only one of the endportions. The opposite respective end portions are electricallyisolated. In the illustrated embodiment, the inner and outer tubularconductors 902, 906 are electrically connected to each other via jumperwires 910 at adjacent end portions 902 b, 906 b (FIG. 57C).

In some embodiments, the inner and outer conductors can be formed asthin-film foil layers of conductive material on opposite sides of a thinfilm insulator (e.g., a laminated, thin flexible body).

The RF shields 900 are spaced-apart sufficiently to allow articulationof the shaft 402 and without any stiff points. In some embodiments,adjacent RF shields 900 may be spaced-apart between about 0.1 inches andabout 1.0 inches.

By electrically connecting (i.e., shorting) the inner and outer tubularconductors 902, 906 at only one end and not attaching the conductors toground, each RF shield 900 serves as a quarter-wave resonant choke thatforms an effective parallel resonance circuit at a frequency of interestand/or generates high impedance at the inner shield at the location notshorted. Each RF shield 900 impedes the formation of resonating RF wavesalong conductive members, such as electrical leads and, thus, thetransmission of unwanted RF energy along the shaft 402 at suchfrequency.

Each of the illustrated RF shields 900 can be tuned to a particularfrequency by adjusting the length L of the RF shield 900 and/or thethickness of the dielectric layer 304. Typically, the length L of RFshield 900 is about twenty inches (20″) or less. However, the RF shield900 is not limited to a particular length.

Embodiments of the present invention may be utilized in conjunction withnavigation and mapping software features. For example, current and/orfuture versions of system 10 and ablation/mapping catheter 80 describedherein may include features with adaptive projection navigation and/or3-D volumetric mapping technology, the latter may include aspectsassociated with U.S. patent application Ser. No. 10/076,882, which isincorporated herein by reference in its entirety.

Referring now to FIG. 58, the distal end portion 1106 of an ablationcatheter 80, according to some embodiments of the present invention, isillustrated. The ablation catheter 80 includes an elongated flexiblehousing or shaft 1102 having at least one lumen (not shown)therethrough. The distal end portion 1106 includes an ablation tip 1110having an ablation electrode 1110 e for ablating target tissue. A pairof RF tracking coils individually identified as 1112, 1114, and whichcan be configured to be functionally equivalent to coils 82 c of FIGS.2-3, are positioned upstream from the ablation tip 1110, as illustrated.The illustrated catheter distal end portion 1106 includes a second pairof RF tracking coils 1122, 1124 in spaced apart relationship, asillustrated. The illustrated catheter distal end portion 1106 includes apair of EGM (electrogram) sensing electrodes 1082 positioned between thefirst and second tracking coils 1112, 1114, and a sensing electrode 1082positioned between the tracking coil 1114 and the tracking coil 1122.

The catheter 80 can include at least the following features for reducingundesired heating caused by RF-induced current: a) a “billabong” cableassembly 1200 for the RF conductor C₁ to the ablation electrode 1110 e,and optionally for the electrical conductors (e.g., coaxial cables) C₂to the tracking coils 1112, 1114, 1122, 1124, and the electricalconductors C₃ to the sensing electrodes 1082; b) high impedanceresistors 1300 in communication with the sensing electrodes 1082; and c)self-resonant cable traps 1400 in communication with the tracking coil1112, 1114, 1122, 1124 connections.

The billabong cable assembly 1200 can include at least the RF conductorC₁ and may also include the various cables/conductors (i.e., C₂, C₃)extending through the lumen of the catheter shaft 1102 and connected tothe various components of the ablation catheter 80. In some embodiments,the billabong cable assembly 1200 can include a series of pre-formedback and forth segments 1202 in a serpentine shape (e.g., the variousconductors C₂, C₃ and RF wire C₁ turn on themselves in a lengthwisedirection a number of times along its length). The term “serpentine”refers to a curvilinear shape of pre-formed back and forth turns of aconductor as a subset of a length of the conductor, such as, forexample, in an “s” or “z” like shape, including, but not limited to atleast one flattened “s” or “z” like shape, including a connected seriesof “s” or “z” like shapes or with additional sub-portions of same orother curvilinear shapes to define forward and backward sections of aconductor. The upper and lower (and any intermediate) lengthwiseextending segments of a serpentine shape may have substantially the sameor different physical lengths.

Each of the back and forth segments 1202 are referred to as currentsuppression modules (CSMs). The individual CSMs 1202 have frequencyresponses dependent on length, pitch, and diameter. Responses fromdifferent configurations having good RF safety performance areillustrated in FIGS. 64 and 65. A Billabong coil (composed of many CSMs1202) can be configured to deliver broad spectrum high attenuation asillustrated in FIG. 66.

FIG. 67 illustrates an alternative billabong cable 1200 configured withCSMs having a series of coiled segments coiled in opposite directions.

The billabong cable assembly 1200 has a unique property ofself-cancelling any induced RF current that wants to flow on the cableassembly 1200. At the same time, the billabong cable assembly 1200provides a low loss path for the 500 KHz ablation current which canreach about 800 mA.

The billabong cable assembly 1200 may perform heat management by acombination of mechanisms. For example, each CSM 1202 can have a highimpedance and short length (with respect to the wavelength at MRIfrequencies), thus reducing coupling to the local E fields. A CSM'scharacteristic impedance can also provide tank circuit characteristics,as illustrated in FIGS. 64 and 65. The back and forth winding of eachCSM 1202 results in an increased self inductance of the conductor and abuild up of parasitic capacitance between the various winds. This selfinductance and stray capacitance cause each CSM 1202 to electricallyresonate at a particular frequency. Resonating frequency can be chosento be equal to frequency at which an MRI scanner transmits RF energy.FIG. 64 shows the impedance of a billabong design in which a CSM 1202resonates at approximately 123 MHz, which is the frequency of operationof a 3 T MRI scanner. Design of a CSM 1202 controls the magnitude of theimpedance as well as the resonance frequency. FIG. 65 shows theimpedance developed by a CSM 1202 that is in the range of 6,000 ohm.

Multiple CSMs 1202 in series along the length of the device cancelpropagating current by phase cancellation between alternate CSMs 1202.Also, multiple CSM billabong conductor/transmission lines have a lowpass filter characteristics, such as shown in FIG. 66 (e.g., attenuatesRF transmission of frequencies>50 MHz). In addition, the alternatinglayers of a CSM 1202 coiled in opposite directions provide cancellationof common mode current deposited on the CSM conductors. For thebillabong design, the coil diameter, pitch and parasitic capacitanceresulting from the wound wires affects electrical properties (impedanceand peak frequency) for a given CSM length.

In some embodiments, the billabong cable assembly 1200 is a single layerbillabong assembly, as illustrated in FIG. 67. The illustrated billabongassembly is a conductor having a plurality of closely spaced conductorportions in a serpentine shape.

EGM signals are detected by the sensing electrodes 1082 that are inclose proximity to cardiac tissue. High impedance (e.g., 5 Kohm orgreater) resistors 1300 are used to isolate the sensing electrodes 1082from the conductor that connects the electrode assembly to ECGamplifiers. Exemplary resistors 1300 are nonmagnetic thick or thin filmsurface mount types of resistors. ECG amplifiers have very high inputimpedance (1 MegaOhm), therefore there is negligible signal loss due to5 Kohm resistors. However, resistors 1300 at the sensing electrodes 1082provide significant impedance to any RF induced current that might wantto flow through the sensing electrodes 1082 to the surrounding tissue.

The tracking coils 1112, 1114, 1122, 1124 detect MRI signals in the RFsignals. In order to preserve the integrity of a detected MRI signal,the MRI signal is transmitted down the catheter shaft 1102 using, forexample, 50 ohm coaxial cables. In some embodiments, a tracking coilcoaxial cable has a 46 AWG, 50 ohm conductive center conductorsurrounded by a dielectric layer, and a conductive shield enclosed by aninsulating jacket. The coaxial cables C₂ isolate the RF signaltransmitted via the coaxial cables C₂ by concentrating the RF signalbetween the center conductor and the enclosing shield of a respectivecoaxial cable C₂. The center conductor of a respective coaxial cable C₂is isolated from outside effects, but the shield of the coaxial cable issusceptible to conducting induced RF currents. As such, according tosome embodiments of the present invention, self-resonant cable traps1400 are utilized with the conductors C₂.

Referring to FIG. 59, an example of a self-resonant cable trap 1400 isillustrated in more detail. A high impedance point on a coaxial cableshield is created by winding the coaxial cable C₂ as a solenoid suchthat the inductance of the shield increases to a point where the straycapacitance and the inductance self-resonate at the scanner frequency ofoperation, which is 128 MHz for a 3 T MRI scanner. In some embodiments,each self-resonant cable trap 1400 is a 60 turn inductor. The 60 turninductor has the frequency response of a low pass filter. However, othernumbers of turns are possible, typically between about 20-100 turns;according to embodiments of the present invention.

Winding the coaxial cable C₂ as a solenoid (e.g., 60 turns) developsinductance on the shield of the coaxial cable C₂ while the signalstraveling inside the coaxial cable C₂ do not see any change. Thisexternal inductance prevents RF currents from flowing externally on theshield of the coaxial cable C₂ through the tracking coils (1112, 1114,1122, 1124) thereby reducing local heating around the tracking coils(1112, 1114, 1122, 1124).

In order to further isolate the conductors (e.g., C₁, C₂, C₃) in anablation catheter 80 from RF currents induced by the MRI coil, afloating balun or RF shield 1500 (FIG. 60) may be embedded within asheath 1600, such as an introducer sheath. An ablation catheter 80 canbe then fed through the lumen 1602 of the sheath 1600, as illustrated inFIG. 61. The illustrated RF shield 1500 includes an inner electricalconductor 1502 (e.g., a conductive braid) and an outer electricalconductor 1504 (e.g., a conductive braid), separated by a dielectricinsulator 1506. At one end 1500 b of the RF shield 1500, the inner andouter conductors 1502, 1504 are shorted (i.e., electrically connected).At the other end 1500 a, the inner and outer conductors 1502, 1504 arenot connected (i.e., the inner and outer conductors 1502, 1504 are opencircuited).

In some embodiments of the present invention, the length L of the RFshield 1500 is selected to equal one quarter lambda (¼λ) wavelength ofthe MRI scanner frequency of operation. Taking into account the effectof electrical insulation on top of the outer conductor 1504 and thethickness of the dielectric insulator 1506 between the inner and outerconductors 1502, 1504, the length L is approximately forty eightcentimeters (48 cm) for a sheath having an inside diameter of ten French(10 F).

Because the inner and outer conductors 1502, 1504 are shorted at one end1500 b and open circuited at the opposite end 1500 a, induced RFcurrents encounter high impedance at the shorted end and cannot flow onthe outer conductor 1504. Moreover, because the outer conductor 1504 iselectrically conductive, RF currents are prevented from penetratingthrough to the inner conductor 1502 and the central lumen of the sheath1600. As such, the RF shield 1500 isolates the portion of conductors(e.g., C₁, C₂, C₃) within an ablation catheter 80 that are surrounded bythe RF shield 1500.

An exemplary RF shield 1500, according to some embodiments of thepresent invention, is illustrated in more detail in FIGS. 62A-62C. Theillustrated RF shield 1500 is embedded within a wall W of a sheath 1600and has opposite end portions 1500 a, 1500 b. FIG. 62A is a perspectiveview of the RF shield 1500, and FIGS. 62B and 62C are respective endviews of the RF shield 1500. The illustrated RF shield 1500 includes anelongated inner tubular conductor 1502 having opposite end portions 1502a, 1502 b. An elongated dielectric layer 1506 coaxially surrounds theinner tubular conductor 1502, and an elongated outer tubular conductor1504 coaxially surrounds the dielectric layer 1506 and has opposite endportions 1504 a, 1504 b. The inner and outer tubular conductors 1502,1504 are electrically connected to each other (i.e., shorted) at onlyone of the end portions. The opposite respective end portions areelectrically isolated from each other. In the illustrated embodiment,the inner and outer tubular conductors 1502, 1504 are electricallyconnected to each other at adjacent end portions 1502 b, 1504 b. Endportions 1502 a, 1504 a are electrically isolated from each other.

In some embodiments, the internal diameter D₁ of the sheath 1600 mayrange from between about 0.170 inch and about 0.131 inch; however, otherdiameters are possible. An outer diameter D₂ of the sheath 1600 mayrange from between about 0.197 inch and about 0.158 inch, and typicallybetween about 5 French and about 12 French (0.066 inch-0.158 inch);however, other diameters are possible. Exemplary thicknesses of theinner and outer conductors 1502, 1504 may be between about 0.01 inch andabout 0.05 inch; however, other thicknesses are possible. Exemplarythicknesses of the dielectric layer 1506 may be between about 0.005 inchand about 0.1 inch; however, other thicknesses are possible.

The thickness of the sheath wall W can be relatively thin, such asbetween about 0.01 inches and about 0.03 inches; however, otherthicknesses are possible. The diameter and length of the sheath 1600 mayvary depending upon the patient and/or the procedure for which thecatheter 80 is being utilized. Embodiments of the present invention arenot limited to any particular sheath size, length, or wall thickness ofa medical interventional device. The sheath 1600 can comprise MRIcompatible material, such as flexible polymeric material. Various typesof polymeric materials may be utilized and embodiments of the presentinvention are not limited to the use of any particular type ofMRI-compatible material. In some embodiments, the sheath proximal end1500 b may be connected to a hemostasis valve (not shown) that isconfigured to prevent or reduce blood loss and the entry of air, aswould be understood by those skilled in the art of the presentinvention.

The inner and outer tubular conductors 1502, 1504 may be electricallyconnected in various ways known to those skilled in the art of thepresent invention. In the illustrated embodiment, the inner and outertubular conductors 1502, 1504 are electrically connected via a pair ofjumper wires (or other conductive elements) 1510 (FIG. 62C). Jumperwires 1510 may be braided wires (e.g., copper wire, copper-plated silverwire, etc.) in some embodiments of the present invention. In otherembodiments, the inner and outer tubular conductors 1502, 1504 may beelectrically connected by allowing one of the adjacent end portions 1502a, 1504 a or 1502 b, 1504 b to contact each other.

The inner and outer tubular conductors 1502, 1504 may be formed fromvarious types of non-paramagnetic, conductive material including, butnot limited to, conductive foils and conductive braids. In someembodiments, the inner and outer conductors 1502, 1504 can be formed asthin-film foil layers of conductive material on opposite sides of a thinfilm insulator (e.g., a laminated, thin flexible body). An exemplaryconductive foil is aluminum foil and an exemplary conductive braid is acopper braid. In some embodiments, the inner and outer tubularconductors 1502, 1504 may be formed from a film having a conductivesurface or layer. An exemplary film is Mylar® brand film, available fromE.I. DuPont de Nemours and Company Corporation, Wilmington Del.

Referring now to FIG. 63, the sheath 1600 of FIG. 61 may include aplurality of RF shields 1500 coaxially disposed within the wall Wthereof in end-to-end spaced-apart relationship. Although a pair of RFshields 1500 are illustrated in FIG. 63, it is understood that manyadditional RF shields 1500 may be coaxially disposed within theelongated sheath wall W in end-to-end spaced-apart relationship. Onlytwo RF shields 1500 are shown for ease of illustration. The RF shields1500 are spaced-apart sufficiently to allow articulation of the sheath1600 and without any stiff points. In some embodiments, adjacent RFshields 1500 may be spaced-apart between about 0.1 inches and about 1.0inches. For example, adjacent RF shields 1500 may be spaced apart 0.1inch, 0.15 inch, 0.20 inch, 0.25 inch, 0.30 inch, 0.35 inch, 0.40 inch,0.45 inch, 0.50 inch, 0.55 inch, 0.60 inch, 0.65 inch, 0.70 inch, 0.75inch, 0.80 inch, 0.85 inch, 0.90 inch, 0.95 inch, 1.0 inch, etc.Moreover, all adjacent RF shields 1500 may not be spaced apart by thesame amount in some embodiments of the present invention. In addition,embodiments of the present invention are not limited to the range of 0.1inch to 1.0 inch. Other ranges are possible according to someembodiments of the present invention.

In some embodiments of the present invention, one or more RF shields1500, as described above, may be coaxially disposed within the elongatedflexible shaft 1102 of the catheter 80.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims. Thus, the foregoing is illustrative of the present invention andis not to be construed as limiting thereof. Although a few exemplaryembodiments of this invention have been described, those skilled in theart will readily appreciate that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention as defined in the claims. Therefore, it is to be understoodthat the foregoing is illustrative of the present invention and is notto be construed as limited to the specific embodiments disclosed, andthat modifications to the disclosed embodiments, as well as otherembodiments, are intended to be included within the scope of theappended claims. The invention is defined by the following claims, withequivalents of the claims to be included therein.

That which is claimed is:
 1. An MRI-compatible catheter, comprising: anelongated flexible shaft having a distal end portion, and an oppositeproximal end portion; an electrical connector interface held by theflexible shaft and configured to be in electrical communication with anMRI scanner; an ablation tip at the flexible shaft distal end portion,wherein an RF conductor extends longitudinally within the flexible shaftto the electrical connector interface and connects the ablation tip toan RF generator, wherein the RF conductor includes a series of back andforth segments along its length; at least one RF tracking coilpositioned adjacent the distal end portion of the flexible shaft,wherein the at least one tracking coil includes a conductive leadextending between the at least one RF tracking coil and the electricalconnector interface and configured to electrically connect the at leastone tracking coil to the MRI scanner; at least one self-resonant cabletrap in communication with the at least one RF tracking coil; at leastone sensing electrode at the shaft distal end portion; and at least onehigh impedance resistor in communication with the at least one sensingelectrode.
 2. The catheter of claim 1, wherein the conductive leadincludes a series of pre-formed back and forth segments along itslength.
 3. The catheter of claim 1, wherein the conductive lead is acoaxial cable.
 4. The catheter of claim 1, wherein the at least one RFtracking coil comprises a plurality of tracking coils, each attached toa separate conductive lead, and wherein each conductive lead includes aseries of back and forth segments along its length.
 5. The catheter ofclaim 1, wherein the at least one self-resonant cable trap comprises aninductor having between about twenty (20) turns and about one-hundred(100) turns.
 6. The catheter of claim 1, wherein the conductive lead hasa length sufficient to define an odd harmonic/multiple of a quarterwavelength of an operational frequency of the MRI Scanner.
 7. Thecatheter of claim 1, wherein the ablation tip comprises platinum.
 8. Thecatheter of claim 1, wherein the at least one RF tracking coil comprisesbetween 1-10 coil turns.
 9. The catheter of claim 1, wherein the atleast one RF tracking coil has a length along a longitudinal directionof the catheter of between about 0.25 mm and about 4 mm.
 10. Thecatheter of claim 1, further comprising at least one fluid exit port atthe flexible shaft distal end portion, wherein the at least one fluidexit port is in fluid communication with an irrigation lumen thatextends longitudinally through the flexible shaft from the at least onefluid exit port.
 11. The catheter of claim 1, wherein the at least oneRF tracking coil comprises a plurality of tracking coils, each attachedto a separate conductive lead, and wherein each conductive lead has alength sufficient to define an odd harmonic/multiple of a quarterwavelength of an operational frequency of the MRI Scanner.
 12. Thecatheter of claim 1, wherein the at least one RF tracking coil is incommunication with a circuit configured to stabilize a tracking signalgenerated by the at least one RF tracking coil.
 13. The catheter ofclaim 12, further comprising a handle attached to the flexible shaftproximal end portion, and wherein the circuit is located within thehandle.
 14. The catheter of claim 1, further comprising a sheathsurrounding at least a portion of the elongated flexible shaft, whereinthe sheath includes at least one RF shield coaxially disposedtherewithin, the at least one RF shield comprising: elongated inner andouter conductors, each having respective opposite first and second endportions; and an elongated dielectric layer of MRI compatible materialsandwiched between the inner and outer conductors and surrounding theinner conductor, wherein only the respective first end portions of theinner and outer conductors are electrically connected, and wherein thesecond end portions are electrically isolated.
 15. The catheter of claim14, wherein the inner and outer conductors comprise conductive foil,conductive braid, or a film with a conductive surface.
 16. The catheterof claim 14, wherein the at least one RF shield comprises a plurality ofRF shields in end-to-end spaced-apart relationship.
 17. The catheter ofclaim 1, further comprising at least one RF shield coaxially disposedwithin the flexible shaft, the at least one RF shield comprising:elongated inner and outer conductors, each having respective oppositefirst and second end portions; and an elongated dielectric layer of MRIcompatible material sandwiched between the inner and outer conductorsand surrounding the inner conductor, wherein only the respective firstend portions of the inner and outer conductors are electricallyconnected, and wherein the second end portions are electricallyisolated.
 18. The catheter of claim 17, wherein the inner and outerconductors comprise conductive foil, conductive braid, or a film with aconductive surface.
 19. The catheter of claim 17, wherein the at leastone RF shield comprises a plurality of RF shields in end-to-endspaced-apart relationship.